Trouble with KVM after upgrade to bookworm

Hello. I use Debian as KVM host for the various VMs (Ubuntu, FreeBSD, no Debian) which serve my home network. I've been doing this since Debian stretch. Until bookworm, each release upgrade has been tedious, but boringly unremarkable. This upgrade seems to have broken KVM so as to cause one or

Trouble with KVM after upgrade to bookworm

Hello. I use Debian as KVM host for the various VMs (Ubuntu, FreeBSD, no Debian) which serve my home network. I've been doing this since Debian stretch. Until bookworm, each release upgrade has been tedious, but boringly unremarkable. This upgrade seems to have broken KVM so as to cause one or