Patches for Ubuntu Mantic have been discussed and approved:
https://bugs.launchpad.net/ubuntu/+source/blender/+bug/2029503 Patch available: https://git.launchpad.net/~ahasenack/ubuntu/+source/blender/tree/debian/patches/0004-fix-support-ffmpeg6.patch?h=mantic-blender-ftbfs-ffmpeg6