A month-or-so ago, FreeNAS annouced that they were merging with TrueNAS a separate project by iXSystems, which is very similar to FreeNAS.
As a result, I had to come up with a plan to migrate from FreeNAS to TrueNAS. I decided my best route would be to do a ZFS replication-based migration from FreeNAS to TrueNAS using the built-in replication tools (Thanks CraftComputing)
After doing so, I attempted, several times, to migrate my NextCloud install from my FreeNAS VM to my TrueNAS VM, but it kept throwing errors, and was unable to be upgraded, so I ended up rebuilding it entirely.
Another thing that was put into consideration was data-redundancy, and protection. I ended up moving my NAS solution from my R410 to my R710 for RAID-based protection, as my R410's storage was a mix of random drives.
In the end, I had upgraded to TrueNAS 12.0 and NextCloud 19, a total success, and no important data was lost in the migration. 👍