Link options no longer working — WordPress 5.5

I upgraded to 5.5 today and link options no longer work. In particular:

* When I click on a link (a website address) in the editor window (I use the classic editor), and then click the edit option, and then click the gear symbol for “link options,” the usual pop-up box does not appear.
* The only change that happens when I click “link options” is that the scroll bar at the far right edge disappears.

Any advice?

I’ve disabled plugins and that doesn’t seem to be related. I’m guessing it’s a 5.5 issue.

Thanks!

The page I need help with: [log in to see the link]