Linux Setup

Compiled by Man Gan, revised by Snott & Doc:

Steps:

Get Perpetuum Steam Client (https://store.steampowered.com/app/223410/Perpetuum/)
Download and install (default steam directory)
Ensure the presence of a steam_appid.txt file with content 223410
Make a copy of the folder Perpetuum somewhere else
Login to Steam (you must now be logged in to use the client), now here comes the difference from the Windows Setup.
Install multiple recent (max 5) versions of Proton either
- Through Steam or
- Manual Installation or
- Compilation.
Add clients to Steam as "Non-Steam" games (select Perpetuum.exe in each)
Force each client to use a different version
- Each client must use a different version or it will not be able to run
Run the copies of Perpetuum with the new links in the Steam Library
- Start the real Steam Application first, and then the copies

Just because you select the new Proton version in the Steam Settings and restart DOES NOT mean it is installed. You must launch the game at least once with the version selected to install it.
Make sure the real Perpetuum Steam App is launching correctly before you copy it
If your real Perpetuum Steam App is not launching, use the option to start it in Safe mode
Remember that since Wine 5.0 and Proton 5.0; the DirectX 9 (and newer, incl. 12) emulation is now handled by Vulkan API, instead of OpenGL API. If you don't have a Vulkan supporting GPU, then your multiboxing options will be more limited. In this case, try adding "PROTON_USE_WINED3D=1 %command%" in Launch Options in each copy, including the main one.
Some version of proton may show an empty text box with only a red warning symbol in it. The solution/fix for it is to do "sudo apt install libfreetype6:i386" (for Debian\Ubuntu-based systems) -sumbitted by CorgiHero

From Steam Library:
- 5.0-9
- 4.11-13
- 4.2-9
- Any newer Proton should run as well, provided your GPU can run Vulkan API, both by hardware and software.
Pre-Compiled from Glorious Eggroll
- Proton-5.9-GE-5-ST
- Proton-5.9-GE-4-ST