Chrome, Safari, and Airmail have stopped trusting random certificates, including Google- and Let's Encrypt-issued

I had this problem (I’m OP of one of the linked threads). I upgraded from High Sierra to Catalina earlier this summer, and have not had this problem since then.

I did an inline upgrade, so any potential “junk” I might’ve had that could interfere, should theoretically still be present. However, it still works, showing that this clearly is a problem with MacOS and how it handles CTs (somewhat described here)