Now that dh-python has been fixed, #976597 can finally be fixed in xen.
With this MR on my test build the dependencies of xen-utils changed from
Depends: libc6 (>= 2.29), libncurses6 (>= 6), libtinfo6 (>= 6), libxencall1, libxenevtchn1, libxengnttab1, libxenmisc4.14, libxenstore3.0 (>= 4.2~), libxentoollog1, libyajl2 (>= 2.0.4), python3, xen-utils-common (>= 4.14.3-1)
to
Depends: libc6 (>= 2.29), libncurses6 (>= 6), libtinfo6 (>= 6), libxencall1, libxenevtchn1, libxengnttab1, libxenmisc4.14, libxenstore3.0 (>= 4.2~), libxentoollog1, libyajl2 (>= 2.0.4), python3:any, python3 (<< 3.10), python3 (>= 3.9~), xen-utils-common (>= 4.14.3-1)
Additionally a /usr/share/python3/runtime.d/xen-utils-4.14.rtupdate file gets automatically added by debhelper as well as well as some hooks in preinst and postrm scripts to handle byte compilation of python source files in /usr/lib/xen-4.14/lib/python.