I have generated my own SSL cert using openssl. The same cert worked on iOS 17. With iOS 18, I open the certificate in Safari and import it on the iPhone. I get "The authenticity of "mydomain.com" cannot be verified." To which I then click Install. But when I go to trust the cert, it does not show up. I use NextDNS and when I import their cert, it DOES show up to be trusted as a root CA. Something has changed to make this no longer work with self generated certs.

iosNumberOne said: Currently, the only workaround is to reset the entire phone and not >use the migration feature or upgrade from iOS 16 or earlier to iOS 18. >Only then will the certificate display correctly in the Full Trust list. I'm >not sure if this bug will be fixed. This isn't entirely accurate. It does not work when updating from iOS 17 to 18. Had this issue on an iPhone 15 Pro and an iPad Pro 11". The existing cert and process had been used as far back as iOS 16 and it worked fine. DTS Engineer said: As I mentioned earlier, installing self-signed leaf certificates it >definitely taking your off the beaten path and I recommend that you >not do that. Instead, set up a test CA and have it issue your leaf. While this did work, generating my own CA and then using a cert generated from that, this was not a requirement with prior iOS versions. It needs to be spelled out in the upgrade notes if this is now a requirement. Previously, I would remove and reinstall the cert (without CA) for the last two years if it needed to be regenerated. This no longer works and is an extra step to have your own CA.