MacOS 10.15.4. Roon client 537. Late-2013 MacBook Pro with only integrated graphics.
I’ve not read about this issue, searches come up dry, occasionally with Now Playing view up, the X in the left hand corner stops responding and I’m not able to close the view. If I select DSP, or Apple icon in the Mac top left and choose About Roon, the About screen comes up, and the screen will change and I can then get back to Overview or elsewhere.
This is more of a an FYI as I have a work around and it only occurs ~10% of the time.