Save for Web Error after Photoshop update 21.2.4 on macOS 10.15.7

Hi everyone - I've seen a pretty long thread on here about people having problems with this - but it seems most of those people were using versions of Photoshop earlier than mine.

Today I updated Photoshop to version 21.2.4. (Mac) Immediately after I was no longer about to save to web image files - something I do pretty much all day every day.  Yesterday I also updared the Mac OS to Catalina 10.15.7 - this didn't create problems though - it was after todays PS update.

For the sake of sanity I tried a few of the suggestions I'd read about - Privacy settings / accessability etc - restarted, and didn't help.

In my case, from an open jpg image file, when I click for save for web, I don't even get the usual save for web window - I just got a system window (see attached), saying 'Error - The Operation could not be completed.  An unknown operating system error has occured'.

Desperate for ideas as this is critical for my daily work.

Thanks everyone

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