I’m still newish to gaming on Linux but from what I’ve heard Nvidia drivers are hit or miss but much better then they used to be. AMD graphics are well supported and using a mix of Proton though Steam and Wine I haven’t really had any issues with games. I have an ROG Ally running Bazzite and a gaming PC running Vanilla OS 2, both do just fine. Additionally hosting game servers on my Debian server has been fine as well.
If you’re on the fence I’d recommend installing on a separate drive and giving it a try.
You can still install other game stores such as Epic or GOG and add games to the SteamOS gaming mode. Autoflatpak also works for that as well. I don’t have the steam copy of FFXIV but no issue, I added it to my library without issue.