Tested on Manjaro Linux, 2023-09-25.
Proton version is the latest one (Proton-Experimental).
Gothic version is workshop - Workshop Beta branch.
This guide should work for any Gothic version on any Proton version, as long as the game launches.
This guide assumes you know how to install packages for your Linux distribution.

to let Steam create wine(proton) prefix to work with.

By default, proton doesn't have directmusic installed. You need to install it on your own.
At first, install protontricks.
Then, install directmusic by running this command in the terminal:
That's it, pretty simple.

The magic number is the steam id of the game, which is also used as the name of the wine(proton) prefix in the steamapps/compatdata directory.
If something goes horribly wrong, you can delete wine(proton) prefix, launch the game to let Steam recreate it, and try again.

Add this to the launch options in the game properties:

Add this to the launch options of the game:
It is assumed, that you use it together with pulse latency override.