TL;DR
A demo for the 1960s Eastern Europe inspired shooter SAMOPAL Protocol is available and reportedly works well with Proton 11 on SteamOS and Linux.
A demo for SAMOPAL Protocol is now available. The fast-paced, skill-based shooter is inspired by classic arena shooters and features a setting based on 1960s Eastern Europe. Players navigate industrial zones, experimental areas, and various districts of a dead city to uncover a narrative through environmental storytelling and recovered memories. Reports say the demo should work well using Proton 11 to run the Windows game on SteamOS or Linux.
Samopal Protocol · official art via IGDBMore on Linux gaming

