I see that you both have an AMD Card. My rig is NVIDIA. It could potentially have something to do with the AMD Drivers although the game was developed originally on a computer using AMD Radeon 5700 HD and FPS was certainly nowhere near that low. Very strange.
I've had a few people message me privately about other aspects of the game so this issue isn't happening for everyone which I guess is good overall but makes it a little harder to localize whatever this specific issue is.
Is it possible that an anti-virus program is flagging the game in some way?
In the main game folder there's a file called "Package.Json". There's a line there that says "chromium-args": "--ignore-gpu-blacklist",
Could you try deleting the part that says --ignore-gpu-blacklist
Usually it's recommended to add that command to help with performance but I'm just curious if it will improve your games performance at all once removed instead.
I'll keep looking and thank you both for posting this issue.