It's not uncommon in general emulation to need tweaks for different games, and they already figured those out. If they can get their old games running on Xbox One, One X, Series S and Series X it means they can consistently keep them working across multiple different configurations. At this point, they are perfectly capable of handling a full PC release of these titles if they wanted to. You are getting too caught up in particularities that just don't change the conclusion.
It's not like they'd release a standalone all-purpose emulator. More likely they'd bundle the games with setups that are already tweaked for those particular games. Just as they would need to for Nintendo games. Even Nintendo itself had to do that. The initially flawed Ocarina of Time Switch Online release comes to mind.
It still makes more sense to assume that if Microsoft is not interested in doing it for their own games, there is no reason to assume they would do it for any others.