Downgrading the packages from src:obs-studio and src:ffmpeg to the previous versions on snapshot.debian.org (30.1.2+dfsg-1+b2 and 6.1.1-5+b1 respectively) resolves the issue, so either one of these updates seems to be the cause here.
The previous obs-studio package is not installable without downgrading ffmpeg due to the ffmpeg transition.
