Hi, I had the same problem but solved it by updating TrueNAS through its own panel.
My situation:
Fresh install of HexOS, tried to install NextCloud but had the same issue as described above by Chrizzle.
I logged in to TrueNAS panel and updated on TrueNAS SCALE ElectricEel 24.10 [release] Train to version ElectricEel-24.10.2.2.
Afterwards I successfully installed Nextcloud without any issues and HexOS deck is working perfectly too.