I just finished the bisection in https://salsa.debian.org/utopia-team/pipewire.git and found the commit dcccfcab7 is the first to cause the problem.
Reverting these commits fixes the problem in 1.4.0-1 90f8b0e40 spa: acp: remove some strictly not necessary SplitPCM properties BAD dcccfcab7 spa: acp: get and emit UCM information for SplitPCM devices BAD Bert Karwatzki
