but on custom roms it works just fine?

Samsung hasn’t fixed it, because there’s nothing to fix, as this is Google’s intention. The gestures work but are very finnicky and the animations are laggy or don’t play at all. Xiaomi decided that they don’t want this so they disabled gestures with third party launchers.

Gestures of Lawnchair work fine here on Lineageos 20 (Android 13).

I’m using Nova with gestures on my Pixel and it works perfectly. This is pretty close to base Android.

On android 13 and my gestures work fine.

Gestures were broken in android 11, but Google had released a fix, so they worked with 3rd party launchers. Xioami, for some reason, hasn’t applied that fix, so it’s still broken in miui. Other roms do not have this issue.

Never had a problem on my pixel with Niagara.