It has been a while since I tried to install Zerotier on my router but it was there at that time. I no longer see it listed in the packages.
v26.1.11_3-amd64
I don't see any mention here of this package causing a problem or being excluded.
Did I miss something?
Is there a solution (manual installation)?
There is a button called Community Packages or something like that : Is it Enabled in your case ?
I don't use that part of OPNsense much but you will figure it out once you see it :)
Activating the community plugins changed recently.
Scroll down to the bottom of the plugins page and you will see the link Click to view the community plugins.. Click on it and you will find it at the bottom of the list.