Videos with projection and screen set as flat mono do not work via API.
Workaround is to open any video from local storage, then flat mono videos loaded via API works. Looks like something is not initialized when using API first, only when starting playback from local.
Platforms: Windows 11, Oculus Quest 2.
As Janek said, the geometry dash workaround is to start the movie in "file browser" and choose 180 mono manually. After that, everything should work as it should.