Thanks again, @softraid-support, my instinct was right. <laugh>

I'm back... The RAID5 array had three HFS+ volumes. One for Mac mini Time Machine, one for MBP TM (not currently used), one for work space when movi...

Thank you, thank you, thank you! I was able to format the volume to APFS using the beta, but still couldn't get the volume to mount. Got distract...