Duplicate of Shotcut 20.07.11 Linux rendering "failed to load producer"
AppImage will fail as well. An older version might work as well as Flatpak.
I just found something:
$ find /snap/shotcut -name 'libpulse*'
/snap/shotcut/x12/Shotcut.app/lib/libpulse-simple.so.0
/snap/shotcut/x12/Shotcut.app/lib/libpulse.so.0
/snap/shotcut/x12/Shotcut.app/lib/libpulsecommon-8.0.so
/snap/shotcut/x11/Shotcut.app/lib/libpulse-simple.so.0
/snap/shotcut/x11/Shotcut.app/lib/libpulse.so.0
/snap/shotcut/x11/Shotcut.app/lib/libpulsecommon-8.0.so
BUT NOT /snap/shotcut/current, which is odd because it is in the portable tar, and the snap and AppImage is built from the portable tar. I suppose the snapcraft tool is removing those now. As a result, for snap, the newest version uses the system PulseAudio libraries.