Music app: Cloud Music Library update fails with error 4010

I'm running OS 26.1, and the Music desktop I am consistently getting "The Cloud Music Library can't be updated right now. An unknown error occurred (4010)."

So, what is it, "unknown error", or a 4010?

Anyway, at some point the Sync Library checkbox unchecked itself, and when I try to turn it back on, the library will appear to sync for a while. It will progress from 25-80% and then stops with the error message.

Just to check if it's a network problem (which a 4010 sometimes might indicate), so I tried switching from my wi-fi to my phone hotspot, but I got the same error after the sync spins for a while.

I don't know if it's related, but on my phone Music app settings, I have Cloud Sync turned off -- this is by choice, but, I thought maybe I needed to have Sync activated on all devices in order for it to work on desktop, but, that wasn't the case, I still got the error. So I tried to turn Sync back off, and it actually refused to.

Not sure what is goin on with OS & iOS 26, but something is broken with Music cloud sync.

What can I do to fix the persistent "unknown / 4010" error?