Well, I'm back. I'd been running Zorin OS 16.3, I'd gotten everything set up exactly as I wanted, so I didn't really need (or want) to touch any settings, so I kind of drifted away from the forum.
But, two of my hard drives crashed.
Lesson learned: If you're running ZFS, do not use SMR (Shingled Magnetic Recording) hard drives... the data throughput by ZFS is hard on them.
Unfortunately, finding CMR (Conventional Magnetic Recording) hard drives is difficult. Most manufacturers have gone to SMR. That's bad if you have a lot of non-sequential data you're writing on an SMR drive. The drive write speed slows way down, the drive works harder, the drive eventually fails.
This doesn't just apply to ZFS... if you're gaming, you'll likely experience the same issue.
The same issue (sort of) applies to solid-state drives... ZFS chokes when using SSDs without adequate caching, and ZFS write-wears SSDs faster; so you really need enterprise-grade drives when you're running ZFS.
Anyway, I found 4 CMR drives, 1 TB each, new-in-package (not rebuilt or 'renewed'), and I'll be re-installing Zorin OS 18.1. I'm just waiting on the drives to be delivered.
Right now, I'm running without hard drives, booted from the Zorin OS 18.1 LiveUSB from Ventoy.