I've got Lightroom CC (v3.3) running on a 2018 MacBook Pro running Catalina (10.15.6). Yesterday was the first time that Lightroom wouldn't Quit when choosing that from the Adobe Lightroom menu. I had to Force Quit since I wanted to restart. Today I am having the same issue. I wanted to see if I could identify the cause (and fix!) before going down the path of doing a Force Quit again.
I just tried Cmd+Q several times and that didn't work.
I believe your suggestion was to Quit the Creative Cloud app instead of just Hiding which is how I normally have it (always running for updates and syncing), correct? If so, I did just Quit the app (no longer in the top-right of the menu) and I'm still unable to Quit Lightroom via the menu and trying Cmd+Q.