Sonic 3D - EDuke32 - Steam Deck
Game available from https://www.indiedb.com/games/sonic-t...
Take the download and extract the data file. Extract that one as well.
Take the usr/share/games/sonic3d folder and place it somewhere in your home folder
Take usr/games/eduke32_sonic3d and put it in your newly created sonic3d folder
Add eduke32_sonic3d as a non-steam game with the lauinch arguments of "-g data.grp" and "Steam Linux Runtime" as the compatibility layer.
Voila. No controller support so be sure to use the Keyboard + WASD layout.