Hello @TomyLobo, we're tracking issues with games run with Proton in the Proton issue tracker. Also, we're using one issue report per unofficially supported game title, so I've gone ahead and transferred this issue report to https://github.com/ValveSoftware/Proton/issues/3931#issuecomment-2393714518.
Your system information
Please describe your issue in as much detail as possible:
For details, see repro steps below
Steps for reproducing this issue:
Running it through FlatPak and the permission changes in step 5 are non-negotiable, I'm not giving Steam and all games free reign over my system.
Steam is neither inspecting nor sandboxing the games on its own and I don't want some rogue game to steal my browser cookies or something, so I'm taking what I think are appropriate precautions.