problem
Tested 4.20.0 to 4.20.3 upgrade. I found that the latest systemvm template (4.20.2 in this case) is not getting registered.
This is because updateSystemVmTemplates is empty here, https://github.com/apache/cloudstack/blob/4.20.3.0-RC20260327T1032/engine/schema/src/main/java/com/cloud/upgrade/dao/Upgrade42020to42030.java#L[…]63
I think this will affect any upgrade from a lower version as well.
Later, I built and tested packages with https://github.com/apache/cloudstack/compare/4.20.3.0-RC20260327T1032...shwstppr:fix-4203-sysvmtemp-upgrade?expand=1, and they worked fine for me.