I had a very similar situation to Signature verification failed when running zypper refresh but the solutions there did not work, and no other web search I could find was helpful, and I really tore my hair out for several days, until I finally discovered that my issue was that somehow the “gpg” executable on my laptop had been deleted (and then reinstalling it was a bit of a puzzle as well, with zypper dead in the water, but in the end that part wasn’t too hard).
I wanted to post this scenario in the hope of helping anyone else who might happen to end up in this weird situation. But the issue linked above is closed, and I don’t see any way to reopen/add a comment/request a reopen; on the other hand, I didn’t really think I should open a new topic with an almost identical symptom. Any suggestions on whether/where/how I should post information about this situation and how I ended up diagnosing/solving it?