I haven't tried it on 12.3 but the above method should work and does on 12.2, only problem is runs syncthing 1.18 instead of the latest 1.19.2. TrueNAS Core 13 is supposed to be in stable release in early May 2022, I feel that the jails which never got a ton of love will only continue to get less. If you want the latest and greatest you'll probably need to consider making the jump to TrueNAS Scale and install TrueCharts catalog and run some docker!Any one found a solution to install Syncthing in a jail with 12.3-RELEASE-p5
I am running TrueNAS-12.0-U8.1