OpenNMS Horizon 23.0.4 is an update to Horizon 23.0.3.
It contains a number of bug fixes including fixes for number handling in ReST interfaces, a possible deadlock in Alarmd, a workaround for looping SNMP agents, and more.
For a high-level overview of what's changed in OpenNMS 23, see What's New in OpenNMS 23.
The codename for 23.0.4 is Morgan le Fay.