Quinn resent the two messages that got lost while I was on vacation. I reran his debug app with a clean account that included the paired key and certificate but not recognized as a secure identity. I sent the results to him but I don't think they help. Status as of Oct 30 2026 is this is a weird signing problem on my Mac and very few, if any, others. A similar problem was reported and he resolved it by doing a clean new setup rather than from a Time Machine backup.

Did you set up your M5 Macbook using a time machine backup from an older Mac? If you did a clean new setup that would eliminate time machine backup as the source of the problem. I used a backup from an M2 Mac Mini to set up my M4 Mac Mini that does not trust valid certificate - private key pairs. My problem has persisted through many Mac OS updates and only occurs on this M4 Mac Mini. --JMB