Mao agrees when Stalin requests that the Chinese Communist forces stay north of the Yangtze in 1949.
Nationalist Chinese forces don't invade Manchuria after the end of WW2 and concentrate on defeating the Communist forces outside of Manchuria.
On whether Stalin tried to get Mao not to cross the Yangtze, I'll recycle an old post of mine:
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There has been much speculation that in 1949 Stalin urged Mao not to cross the Yangtze, but this seems to be based almost entirely on statements by Mao (and one by Zhou Enlai which may be simply echoing Mao) and it is contradicted by the bulk of the evidence. There is a good discussion of this in Dieter Heinzig, *The Soviet Union and Communist China, 1945-1950: The Arduous Road to an Alliance.*, pp. 170-174.
https://books.google.com/books?id=oZntCQAAQBAJ&pg=PA172 For example, Mikoyan (according to his report on his meetings with Mao in Xibaipo) urged Mao to form a government as quickly as possible, "let us say, after the capture of Nanking or Shanghai"--which tacitly assumed Mao would cross the river. (p. 172) Moreover, Mao informed Stalin in mid-January 1949, two weeks before Mikoyan arrived in Xibaipo, of his plans to cross the Yangtze "already that summer." Stalin, who was asked by Mao to say something if he did not approve of any of Mao's statements, raised no objection in his reply or in subsequent telegrams (to the extent they have been published). (pp. 172-3) (In a long telegram in April on "military activities after crossing the Yangtze," Stalin advised the CCP to use caution in advancing to the borders of neighboring states; but the whole telegram is based on the premise that the CCP had already determined to cross the Yangtze, and Stalin did not indicate any disapproval of that decision.) Shi Zhe, who participated in the negotiations with Mikoyan, even claimed that Mikoyan expressly urged the CCP to "free all China completely." (p. 172) Stalin himself never claimed that Mikoyan urged him to stop at the Yangtze, so Mao must have based his assertion that Stalin urged the CCP to stop at the Yangtze on some interpretation or misinterpretation of some Soviet statement or conduct that remains unknown to us. (Also, curiously, when Mao presented Soviet ambassador Iudin in 1956 and 1958 with a long list of Stalin's sins vis-a-vis China--including his 1945 advice to the CCP to avoid civil war--he omitted any mention of Stalin or Mikoyan trying to stop the PLA from crossing the Yangtze in 1949.)
It is undoubtedly true that "Acting President" Lin Zongren (and some other KMT leaders) did hope that Stalin would pressure Mao into stopping at the Yangtze--and into agreeing to a de facto partition--but this seems to have been wishful thinking. "At first glance, statements by a historian from the People's Republic of China appear to support the thesis that Moscow had sought to restrain the PLA from crossing the Yangtze. He claims that Ambassador Roshchin had reached an agreement with President Li Zongren concerning three conditions for Soviet mediation, despite the Moscow declaration--reached under pressure from Mao Zedong--which stated that the USSR would not participate as a mediator in peace negotiations between the CCP and the KMT. He had thereby provided support for Li's attempt to 'set the boundary at the river'...and thus establish 'a Northern and a Southern Dynasty' [*bei nan chao*]. And yet the idea that Roshchin pursued a line that was different from Moscow's should be ruled out. Even if it were possible to find sources to provide evidence of Roshchin's alleged behavior, the resulting conclusion with respect to the *bei nan chao* question would go way beyond its target." (pp. 173-4)
It certainly seems plausible that Stalin would have preferred a North Chinese Communist state which would be weak (and therefore dependent on him) to a Maoist victory in all of China. But that he tried to impose division on China in 1949 remains doubtful--probably he knew that it would be futile to try to get Mao to stop halfway by this point.
https://www.alternatehistory.com/forum/threads/ahc-china-divided-more-evenly.370707/#post-11486892
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It is probably true that Chiang made a fatal mistake getting his forces tied down in Manchuria and that he should instead have followed Wedemeyer's advice to institute reforms and consolidate his position south of the Great Wall. But in fairness to Chiang, Marshall actually encouraged him (initially) to send troops to Manchuria. See Jay Taylor's discussion of this in his biography of Chiang Kai-shek, *The Generalissimo*:
"The State Department’s White Paper, issued in 1949, declared that Chiang’s government “in occupying Manchuria took steps contrary to the advice of competent United States military observers who were aware that the Government could not reoccupy Manchuria and pacify the rest of China.” This claim is one of the most important unexamined, and incorrect, assumptions of the Chinese civil war. Wedemeyer did tell Chiang and the Pentagon in November 1945 that the Nationalists could not win in Manchuria and probably not in North China, but policymakers in Washington did not adopt this point of view. In addition, earlier that year Wedemeyer himself had been optimistic about the Nationalist Army’s prospects for dealing successfully with the Communists in the postwar period, including in Manchuria. Beginning with the negotiations on the Sino-Soviet treaty in the summer of 1945 in Moscow, the United States had made clear it wanted Chiang to take a tough stand in asserting Nationalist China’s sovereignty in Manchuria. After Japan’s surrender, America stood ready to transport almost a quarter million Nationalist soldiers to the region for this purpose and it completed the task during the Marshall Mission. At the beginning of the mission, the firmly, albeit privately, stated policy objective of Truman and Marshall was to support Chiang’s takeover of all of Manchuria while trying to prevent a civil war. To accomplish this goal, the United States sought to promote a coalition government, but did not make such a coalition a quid pro quo of U.S. assistance to Chiang. Marshall at first clearly encouraged Chiang to continue to try to assert his authority throughout the Northeast. Marshall’s original peace plan provided for a huge 14–1 advantage in government troop presence in Manchuria, and gave the Nationalist government the right to deploy its military anywhere in the region in order to establish its authority. Marshall even promised to find surplus winter clothing for the Nationalist troops heading north. As noted earlier, as far back as mid-November 1945, Chiang had decided tentatively to withdraw from Manchuria, but positive Soviet moves and Marshall’s initial steps and statements changed his mind.
"It was not until the spring of 1946 that Marshall began to tell Chiang he could not defeat the Communists in Manchuria, but even then, still believing a genuine coalition was possible, he did not urge Nationalist withdrawal from the region. Prior to Marshall’s arrival, Chiang had ranged from less to more pessimistic about Soviet cooperation in Manchuria and thus about his own prospects in the Northeast, and probably he would have withdrawn if Marshall, during their first meetings, had strongly echoed Wedemeyer’s advice.
"If Marshall had given this counsel, however, and Chiang had agreed, it would have saddled the United States with the responsibility for helping the Nationalists assert and maintain control along a line somewhere south of the Great Wall. America would have been caught up in the enormous civil war over whether there was to be one China under the Communists or two Chinas, and if two, where the lines between them would be drawn. Almost certainly, neither Marshall nor Truman had thought this through; they simply wanted the best of both worlds—to avoid getting caught up in the civil conflict while maintaining a united, non-Communist, non-Soviet, allied China that included Manchuria. Thus they pursued the chimera of the optimal solution: Mao’s abandonment of not only his revolutionary ideology, powerful army, and large territorial and population base, but also his support from China’s superpower neighbor, all in order to serve as junior partner in a democratic government and a truly amalgamated army under the leadership of Chiang Kai-shek.
"Within weeks of Marshall’s arrival, Chiang began to fear that the Americans were headed down the path of appeasing the Communists, and he could have easily abandoned the struggle for Manchuria. It was primarily the Nationalist military victories in 1946 that misled Chiang into thinking he could hold the southern half of Manchuria, and he proceeded to pour in more and more troops for another almost two years, even when, beginning in early 1947, he again recognized that it was highly unlikely he could succeed. During the final and decisive 1948 Manchurian campaign from September to late October, Chiang, as usual, sent detailed instructions to the field commanders and often made it difficult for his senior commanders to give their subordinate generals tactical as well as strategic orders. But according to General Barr, “in spite of this unorthodox procedure,” the plans Chiang made and the orders he gave in the decisive battles for Manchuria in the fall of 1948 “were sound.” Had they been obeyed, the American general concluded, “the results probably would have been favorable.” Barr’s assessment seems highly doubtful given the powerful position the Chinese Communists with Soviet help had established in the region and the financial and moral decay within the Nationalist regime. But it does give some weight to the argument that had Chiang pulled out of Manchuria even as late as the spring of 1948, he might have had enough military strength to hold the line at either the Yellow River or the Yangtze, albeit only with large-scale U.S. military and economic aid."
http://www.thegeneralissimo.net/excerpts.htm