I downloaded OPNsense on the evening of July 14th, so this was version 24.1.10_1 or 24.1.10_2
I installed and updated it, so it was on version 24.1.10_3
Then I tried to install the plugin clamAV, but I received an error message, saying:
***GOT REQUEST TO INSTALL***
Currently running OPNsense 24.1 at Mon Jul 15 18:50:33 CEST 2024
Installation out of date. The update to opnsense-24.1.10_3 is required.
***DONE***
So OPNsense 24.1.10_3 self-identifies as 24.1, and therefore, clamAV (and possibly other plugins) refuses to install.
... aaaaand with today's installation (July 17, 2024), it worked well and installed. This topic can be closed as resolved.