Pages

Restarting the Mac into Safe Mode, and launching Pages while in Safe Mode has been reported as usually clearing out the crud that causes this.

How to use safe mode on your Mac - Apple Support

The Safe mode restart will take longer that a normal restart, and you will notice a degradation of video performance in Safe mode. After launching (and Quitting) Pages in Safe mode, do a normal restart of the Mac.

Regards,

Barry

Regards,

Barry

Or maybe if you can provide a bit more context,

I had the same happened to me when I made the "jump" from El Capitan to Catalina. But in my case it was because it took some time (an hour or so) for App Store to realize it had to update the app. But I don't have the feeling that is what you're talking about?