the tricky bit about Japan is that its so much out of the way that no one really was willing to consider conquest of it (specially since it was also one of the most militarized countries outside the western world), force them to open for trading posts yeah, but not vassalaging it ... Korea was much weaker at this point, and a much better toehold from which you could influence China (the big prize).
Don't think there is any way for Russia to advance their infrastructure enough for them realisticly take a bite without getting more than they can chew
Any European power would first have to seize a significant portion of Japan or China before even thinking about Korea, if at all. Although China, Japan, and Korea all extensively traded with other countries within East and Southeast Asia for centuries, China and Japan both had significant domestic markets as well by the time that the Europeans arrived, while the same did not apply to Korea, as it had a smaller population (10-15 million), and the majority of the urban population had remained clustered around Hanseong (Seoul).
However, even if Europeans had somehow managed to seize Korea, the only region that Europeans could have gained significant access to would have been Manchuria, which only had around 2 million inhabitants (half of which were Han Chinese) in the late 18th century, not to mention that most of its resources could generally have been attained elsewhere. As a result, considering that even Manchuria was not viewed as particularly strategic until the Treaty of Aigun in 1858, when the Russians annexed Outer Manchuria, and Chinese migrants began to flood into Inner Manchuria soon after, Korea would have been viewed as less so. While taking the peninsula could theoretically have facilitated access to Shandong, Southern China as a whole would have remained far more attractive for centuries, making it unnecessary to sail further north just in order to contact Joseon.
IOTL, after a few sporadic shipwrecks for centuries (but no diplomatic contacts), the French only decided to intervene in 1866 (and voluntarily withdrew after minor defeats) specifically in retaliation for the execution of its missionaries, not because it wanted to "open" Korea up to trade. Additionally, while the United States made two minor attempts to contact the peninsula in 1866 and 1871, ostensibly for trade, both were militarily repulsed. These halfhearted contacts were in stark contrast to the Europeans' collective interests in China and Japan, which spanned over three centuries despite the fact that both sought to actively curtail European trade by limiting the number of ports in question.
Ultimately, while Korea's relative "remoteness" caused Europeans to generally ignore the peninsula, over two centuries of extended peace and stagnant economic/social policies meant that its military and economy were relatively fragile when the Japanese gradually intervened after 1876, eventually causing it to fall prey to Japanese annexation in 1910.
I've also detailed Korea and Japan's general situations elsewhere, specifically
here and
here.
