Since their move to the new GSC I have seen far more reports that make no sense, mean nothing to me. I have seen discussions around here suggesting that either GSC innards are making them up or that the malformed URLs were found on some other property/domain likely with no relation to yours. Less reliable tools mean more time spent to determine whether/where they come from. I usually mark it as fixed and they agree after a day or so.

Occasionally I'll paste one in their Inspection tool and see what they find. They have not found any yet when the report involved non-existent URLs.

I've never paid attention to any bogus URL requested by a legitimate crawler, whether reported in Webmaster Tools / GSC or observed in logs. Life is too short to worry about things that have no existence outside the robot's fevered imagination.

OK, take it back, there's one exception: If there's a sudden flurry of requests for nonexistent URLs following some consistent pattern, it may mean that I've goofed in creating internal links. (I can think of two times this has happened in 10+ years.) But these are easy to find, easy to fix.

Thanks for the replies. I did try marking them as fixed and so far the ones that were "rechecked" came back as NOT fixed... As the links in that form certainly don't exist on any of my pages I will just keep an eye on their error report and move on to more constructive things in life than trying to decipher cryptic Google messages...