I have the same issue but in my case steam crashes and the only solution is to either reinstall the proton version that was removed or delete my steam config.
https://github.com/GloriousEggroll/proton-ge-custom/releases)steam/compatibilitytools.d/)I've also reported this issue via steam support but I was sent here.
Nothing extracted yet.
Your system information
Please describe your issue in as much detail as possible:
Games that had custom proton version forced cannot be re-installed without any apparent reason after that custom proton is removed. The UI doesn't explain why the game cannot be installed and the properties dialog has misleading contents.
Steps for reproducing this issue:
.steam/root/compatibilitytools.d/After checking "force the use..." game is installable again.