That’s because plugins are dead and unmaintained. As is 12.4-RELEASE, and any release up to 13.2-RELEASE.
The ultimate solution is to update to the 13.3-BETA2 (or wait a week for the 13.3-RELEASE) and install software in manual jails.
But with IX ditching the BSD world and moving to linux, you might be better off going with TrueNAS SCALE.