I had a very enjoyable experience playing between my Windows PC and steam deck and did most of my playthrough on the deck.

I used xess2.0 mod (https://www.nexusmods.com/finalfantasy7rebirth/mods/15) and set the in-game minimum resolution scale to 66%. Using windowed mode 1280x720 and switching display sync technology to VRR (had a better experience switching off from v-sync dk how).The game is completely playable (though you have to get used to the textute pop-ins) at 30fps 95% of the time with drops especially in cosmo canyon town and the starting nibelheim town (you don't spend a lot of time there and the open world is almost always at 30fps)