the gitlab issue lacks a bit of debug - are you able to run adb logcat from a pc/laptop with cable attached to get the issue a bit of context?
the “provoke L1 to L3 fallback” route is what works for others by getting rid of a library. Will give you less video resolution though - S8: Onleihe App Audiobooks do not work - #6 by tcecyk
To have content allowed for L1 I think you’d need a /e/ Android12 / “S” build that doesn’t exist yet - it would include a fix announced at https://www.xda-developers.com/android-12l-fixes-widevine-l1-bug-pixel-phones/