Not for sure but it looks like it has something to do with the “new” Kernel in the latest OSMC Version
Looking at this link
snd-bcm2835.enable_compat_alsa=1
inside the config-user.txt should also work
With the first new OSMC with Kodi 19 it works, if not some would watch Movies without Sound from the beginning and won’t tell.
May someone can prove me wrong but I would bet with the [2021.11-2] it will work without problems.