Library sync problem (which isn't the problem I need to solve)

I posted this on Monday in the Adobe fonts forum, but got no replies. I posted it on the InDesign forum yesterday, and got some feedback, but nothing that helped. 

Adobe fonts clearly is a feature of ID v. 14.0 (2019), and they work on my machine with Illustrator (2020) but I cannot activate fonts in InDesign -- and, of course, there is no way to upgrade just one iteration, to ID 2020 (if that would even solve the problem). I do see in the CC app an alert, "Something went wrong when initiating Creative Cloud Libraries," and I tried several things suggested on the pages linked to, all to no avail. 

The only clue Adobe provides is an alert in CC telling me of a Libraries Sync Error. I went to the page and tried all four things -- twice, including today -- and nada. 

Screen shots of the actual problem are also attached. And, I'm running Mac OS 10.13.6 (high sierra). Yes, it's old, but everything else on my machine functions, and the system is stable.