I'd hope so and square enix has been... improving, but their track record of ports even working properly on an average windows PC is not super great. I'm still hoping I'm wrong, but betting against it launching in verified status and kinda 50/50 on it working at all on my steam deck.
Probably not fully, unless they actually do work on the games. The cutscenes on some of the games play with a proprietary protocol that even Proton-GE can't run. So, while the game works, the cutscenes don't.
It's feasible that they will fix it, but I consider it highly unlikely.
Do you have any documentation on this you can link because it doesn't really make sense what you mean and I love learning about these things. Most of the cutscenes will be rendered in engine so nothing special there, and the pre-rendered ones if they used an unusual codec I don't get why the codec isn't baked into the game files which would render that also a moot problem.
Okay, that's pretty lame. According to several spots (all quoting an RPGsite writer and an emoji response from a Sqenix dev) square Enix actually brought in a third party company specifically to improve Steam Deck support. Honestly makes sense, the steam deck seems like their largest potential new customer base.