There is a review process for TestFlight?

It’s not possible yet. See this GitHub issue: https://github.com/buresdv/Mlem/issues/61. Personally I use two accounts to avoid this issue like I did on Reddit and do on Twitter.

Why not just CS:GO? But I’m only saying this because I have no real recommendation tbh. For offline I can recommend Ravenfield. It’s really fun even though the native Linux version is kind of broken when using mods which is kinda the point of the game. Works fine using Proton though