Pixel 4a models do have headphone jack if you don’t need the newest models, unfortunately no sd card slot still

Don’t know that kind of site but i would bet Google Pixel phones have one of the best support from custom roms including Lineage, Murena, Calyx, Graphene and whatnot

And Vencord has a desktop client “Vesktop” which works like Webcord, with audio in stream too. No presence detection but notifications have worked for me

Proton is basically just a version of Wine but Steam has other runtime apps like Pressure Vessel that work together making the game run. Don’t know if Lutris has anything else than managing and running the apps in the Wine prefix with specified Wine version. This is as deep as my knowledge goes.