The steam version probably just uses steam features through some library/interface/whatever that simply implements calls to the relevant code depending on the game's build (steamworks for steam, Xbox live or whatever they changed it to again, PSN, epic online services, etc..) for platform-related stuff like rich presence, joining servers etc. I don't know the specifics of R6 but I've worked on multiplayer, multiplatform games, and I really doubt they have a specific network stack for Uplay, another one for PC, and then another one for each console. Especially if it has crossplay.

More likely it's all going to ubi's servers (through their own crossplay solutions and servers, or through a third party like EOS) and just implementing the aforementioned platform specific stuff to make the experience smooth for the end user.

I'm not a law guy but I don't think the other platforms pricing thing was ever about a "steam version" of the game, as that rule would be easily circumvented by releasing another "version" where the black background on the title screen is a slightly different shade of black than the steam version or whatever.