I believe this issue that was raised 2 years ago is the same issue I'm currently experiencing. Whenever using Unity with Built-In Render Pipeline and Post-Process Layer it causes issues with Gizmos and world grid to render in front of everything. I've tried messing with settings and searching for a solution but have not been able to find one. Below video is of a fresh install of Unity 2020.2.4f1 and only package installed is the Post-Process Stack (V2). I tried a 2019 version of Unity and an older version of the Post-Process Stack (V2) and still had the same issues. I don't have this issue with URP but I would prefer not to use that or HDRP at this time. Hoping someone may know of a fix or perhaps there is something I am setting incorrectly?