FWIW, the visibility problem of the Nucleus SSD drive was solved…
I found on the Roon community something about SMB3.1. See link 1 below. That led me to a Microsoft link that not only let me see the Nucleus SSD drive, but also my Apple Time Capsule drive that I hadn’t seen since getting my Win10 laptop last year!
(Windows 10 (newest update), SMB 3.1.1 and Synology) [Roon Software]
Link 2 - This fixed problem…
Meanwhile, I could not see my USB SD card reader hooked up to the Nucleus. I switched the two Nucleus USB connections. I moved Dac from bottom to top, and SD card reader to bottom. This lets me see the SD card in both Win Explorer and Settings - Choose Music Storage Folder. (Faster way to transfer music to Nucleus SSD drive.)
Cheers.