I had issues with and SSD pool as well, what I had to do was log into the treunas side and go to drives, then wipe the ssds in the gui, then create the pool in truenas, it then showed in HexOS.
I think this was due to not being wiped with a lvm locked partition on them prior. BUT I did discover 3 of my 7 SSDs had really bad smart reading and just failed during all this. So take what I said as a may work but my set up had issues.