Followed this page:
https://wiki.zoneminder.com/Raspberry_Pi_4_-_Raspbian
and get 1.32.3
I uninstalled deb-multimedia zoneminder, remarked it out in sources.list, added:
deb https://zmrepo.zoneminder.com/debian/master buster/
apt update and installed zoneminder.
Maybe I need to nuke the DB that I dumped from my existing Xen VM and start over/reconfigure all the rtsp Zero's I'm running (no fun)?