Weird patches of color appear randomly

This issue started with Catalina and has persisted with Big Sur: There are occasions when I resize my window or save or navigate and all of a sudden patches of color appear in my InDesign document: bands or geometric shapes (see attached; the gray triangle and green background, not pullquote block, are what I'm talking about). Typically the colors are ones I'm using in my document, so that's not random. I usually close the document and/or restart the program. I've also restarted and trashed prefs (aaargh) and/or reinstalled on occasion. But it keeps happening. And last night I was working on a document and all of sudden I'm getting text scored through and yellow highlighting (indicating H&J errors — except that feature wasn't highlighted in Composition>Preferences). Anyone know what this might be about? I have a feeling it's a CPU or redraw issue, perhaps a setting is off, but I've not had this before on my 2017 MacBook Pro, which has adequate memory and disc space. I can also say that ID also launches more slowly, with spinning wheeel, on a regular basis, since Catalina. I've deactivated as many fonts as I can (except for those crappy Noto fonts, which one can't deactivate; thanks Apple).