You need to act on either or several of the three drivers of decolonisation: african opposition to european rule, external pressure on european powers to decolonise, and european fatigue leading them to pull out. The problem is that twitching some of them is mutually exclusive with a post-45 POD.
For instance, you can try to generalise the Portugal-path: ideological commitment to upholding the colonial order militarily, tolerated by the US out of anticommunism. For instance, you can imagine that communist insurgencies in 1944-1947 lead to reactionary governments in France and the UK taking power with tacit US consent; those governments would then pour ressources in defending their empires out of prestige/ideological concerns.
Problem 0 with that path: it's a crapsack world for Africans. Problem 1: in OTL, the French *did* pour considerable ressources in defending the Empire in the 50s and 60s; one can consider that with even more efforts, they could have quashed the Algerian insurgency and maaaaaybe kept the Indochina war going, but no ammount of military pressure could turn the tide, and european resistance would probably have collapsed in the late 60s - early 70s. Problem 3: that path reinforces driver 1, native opposition, and makes independances more likely, albeit at a later date.
On the other hand, you can imagine that Communists are more successful than OTL in France, and seek to enfranchise the Africans (which is not a given!). Then, sure, Africans are more ok with staying in, and we can imagine that under a communist government the French public's consent is not going to matter that much - buuut the Americans are going to panic if France goes commie along with half of African, and will probably encourage local independentism.
The problem, then, is that with a post-45 POD we still have a world dominated by two competing ideologies/block, neither of which allows to tune down all three factors.
So we have to imagine that somehow a "3rd way" will arise that wil be acceptable to the Europeans, the Africans, the Soviets, and the US. I don't need to explain why OTL's Europeans didn't find it...
Let's try in their place. The most promising faction to this purpose is the center-left, which were the most liberal in colonial matters (see the Blum-Violette plan), along with black or afropean personalities from the fringes of the communist parties, like Aimé Césaire, who had both the radicalism and, unlike most CP members, the brains necessary. We thus have to prop up these guys into power *and* make sure colonial reforms become an item on their agenda *and* make their rule palatable to the US. .
My proposal for that is a failed communist uprising in France and Italy in 1944 (which they historically considered) leads to the communists becoming weaker and the socialists, having fought against them, becoming both more popular (due to CP collapse + defeating the insurgents + "wait, those guys *don't* want to kill us and eat our bones?" effect on the right) and more effective/compelled to rethinking more of their assumptions (historically, they clung to a lot of outdated marxist rhetoric because the commies were breathing down their necks in every election). Bonus point if, as would be very likely, the insurrection is defeated thank to colonial troops - not only because the socialiss will be grateful and because Thiaroye won't happen, but also because the remaining communists will hate Africans' guts, which will make them more sympathetic to everyone else).
The certitude, then, is that the socialists will double down on their OTL efforts for developping the colonies and extending civil rights there (which they did in OTL to great effect in French Africa), while the 1944-1947 cycle of repression in the Empires will be butterflied away. From there, all the 3 decolonisation drivers will be reduced: the French will (well, might) be ideologically more committed to keeping their empire together, the Africans will have it better (at least at the start), and the US will see no objection to a socialist but anticommunist government safeguarding them against a perceived greater commie threat.
From there, we can envision a range of outcomes : a federalised, decentralised but intact french African empire; integration of some colonies (Gabon, notably) as departments; etc.
Of course, this only concerns directly the French Empire, but we might imagine that more progressive and successful policies in it might get adapted elsewhere.