Hello @superenginegit, are you still experiencing this issue on an up to date system? (https://github.com/ValveSoftware/steam-for-linux/issues/6874#issuecomment-1159450765)
No, it switches that game to the default proton version now. So it's as expected.
Your system information
Please describe your issue in as much detail as possible:
When a custom proton version is deleted all games set to run with this version should be reset to the default steamplay runtime. Instead they are marked as "not installed" but can be recovered by going into properties and changing their steamplay runtime.
Steps for reproducing this issue: