Finally got backups setup on the Mac Studio. Had to expand the Time Machine volume on the TrueNAS server from 4TB drives to some spare 6TB drives I had on a shelf. Gave me just enough extra space to backup another Mac.

Pro tip: Keep your Time Machine backups on separate drives from the rest of your network storage. A handful of Macs backing up every hour really consumes a ton of iops. You don’t want that slowing down the rest of your network storage.