The game starts but thinks it's in trial mode and prompts you with a "buy now" screen. You have no other option than to quit.
Proton Experimental
System info
proton log
Proton 4.2-9 is the only version which lets my past the demo screen. But the performance is very bad, most levels freeze completely very quickly
Recorded with wined3d enabled:
proton-25700.log
@iodream some report success with 4.11-13: https://steamcommunity.com/app/25700/discussions/0/5788831477022202444/
I haven't tried with that version yet. Newer versions fail the purchase check, as you noted. "Thanks for playing the demo -> buy now".
Hello @MayeulC, please add PROTON_LOG=1 %command% to the game's launch options, reproduce the regression, and attach the generated $HOME/steam-$APPID.log to this issue report as a file. (Proton logs compress well if needed.) Also, please copy your system information from Steam (Steam -> Help -> System Information) and put it in a gist, then include a link to the gist in this issue report.
Apparently the latest proton Experimental update fixes the purchase check.
Sorry for not retesting earlier, I did not have access to a computer running steam, I just wrote here some information I found by chance.
I was able to retest, and can confirm that proton experimental fixes the game (tested on Steam Deck).
proton experimentalx3 2023-04proton 4.2-9x1 2022-11proton 3.7x1 2018-08PROTON_LOG=1x1 2023-04
Arch Linux
Kernel 4.18.3
Proton 3.7
bspwm 0.9.5
CPU Intel Core i3-2350m @ 4x 2.3GHz
RAM 4gb
GPU Intel(R) HD Graphics 3000
The game does not start.
https://store.steampowered.com/app/25700/Madballs_in_BaboInvasion/