I remember finding the definitive tinkering post on Thief Gold so I will try my best to imitate it here

For optimal experience:

1. If you can install and launch the game with Steam once
2. Exit the game and Steam (significant)
3. Download T2Fix 1.27e mod version and Thief 2 HDmod 1.0
4. Install T2Fix in terminal

protontricks -c "wine ~/Downloads/T2Fix_1.27e_with_mods.exe" 211740

1. When asked for a path paste this (but replace $USER with yours!):

Z:\home\$USER\.steam\debian-installation\steamapps\common\thief_2

1. Install Thief 2 HDmod in terminal (paste same path as before):

protontricks -c 'wine ~/Downloads/Thief2HDMod1.0.exe' 211740