Most of us had that issue, you can fix it by updating your Revanced Manager to the latest version, downloading the YouTube apk v18.23.35, and patching that one. Then, install your patched version (I didn't need to uninstall my current version) and the issue should be gone.
Probably they are using Complementary Reimagined or BSL. Imo, Complementary Reimagined are one of the best looking shaders in the game, I'll recommend you to try them :)