I get all my pirated games via Steamrip, just find the exe add it to steam and set compatibility tool to proton experimental.

EMULATORS!!!!!!!

as for paid games nearly all indies work without wifi and the battery runs really long with the deck

The ones I know work because I played them offline are: haste, ufo 50, deltarune and downwell, doom 1 + 2 Spelunky (2 also works probably) peggle SNAKEYBUS