You can set steam to boot into big picture mode. I just went through this. Single bazzite user with no password login and auto start steam with multiple profiles for different users in the home. Steam you'll need to set up family library to share games. Most will work in this mode but some won't because they are jerks. If you need Windows you can get bazzite to put a link within steam so you don't even need to set up grub to switch between the different OS's. I can't remember what it's called but if you browse the installed programs you'll see one that says something along the lines of bazzite tweaks or extras or something. Loads of good things in there
Edit: it's called bazzite portal setup. Super handy