So I've tried multiple versions of proton and ProtonGE, but it appears that Dual Universe's EQU8 Anti-Cheat is in one way or another incompatible or not set up to support the Steam Deck file system.

Error I get: "A security product (Anti-Virus, Firewall, Sandbox, etc.) is conflicting with EQU8 Anti-Cheat. 1) Exclude these folders in your security products:

Z:\home\deck.local\share\Steam\steamapps\common\Dual Universe Demo\Bin C:\ProgramData\EQU8\Dual Universe Prod

2) Update security products. 3) Validate your drive with chkdsk.exe 4) Reboot your computer Internal message: "Unable to copy files (1)"."

Devs: is this on your radar? Have you all committed to Steam Deck support?