The same problem still persists in excalibur today.
Versions:

• python3-libvirt (= 10.5.0-1+b1)

• virt-manager (= 1:4.1.0-4)

# apt install virt-manager
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

Unsatisfied dependencies:
 python3-libvirt : Depends: libvirt0 (>= 10.2.0) but 10.0.0-1devuan1 is to be installed
Error: Unable to correct problems, you have held broken packages.

I tried to modify the dependency to libvirt0 in DEBIAN/control of the python3-libvirt package to 10.0.0-1devuan1 which breaks virt-manager.
I also tried to install libvirt0_10.5.0-1_amd64.deb from debian testing which makes virt-manager functional but breaks at least:

• libvirt-clients (= 10.0.0-1devuan1)

• libvirt-daemon (= 10.0.0-1devuan1)

• libvirt-daemon-driver-qemu (= 10.0.0-1devuan1)

• libvirt-daemon-config-network (= 10.0.0-1devuan1)

• libvirt-daemon-config-nwfilter (= 10.0.0-1devuan1)

• libvirt-daemon-system-sysv (= 10.0.0-1devuan1)

I then tried to change the version of libvirt0_10.5.0-1_amd64.deb to 10.0.0-1devuan1 and installing it together with the modified python3-libvirt package, but this breaks too because libvirtd needs the older version of libvirt0:

/usr/sbin/libvirtd:
 /lib/x86_64-linux-gnu/libvirt.so.0:
  version `LIBVIRT_PRIVATE_10.0.0' not found (required by /usr/sbin/libvirtd)

UPDATE:

Based on #2 i found python3-libvirt_10.0.0-1build1_amd64.deb from the Ubuntu archives. Installing this package seems to make virt-manager and qemu-system-x86 work without problems.