I have been using HTTPS decryption in Windows Fiddler for years, to inspect the traffic to and from my app.
And it has been working perfectly on both my Samsung phone with Android 12 and my iPhone 6 Plus with iOS 12.5.5.
Recently I got an iPhone 11 with iOS 15.1, and find myself completely unable to get it to work 😢
Because I know, that requirements for certificates have been strengthened in recent versions of iOS, I have now ended up "resetting" the certificate in Fiddler and creating a new root certificate. I have successfully removed the old certificates and installed the new Fiddler certificate on both the Samsung and the iPhone 6 Plus, following the Capture Traffic from iOS Device guide, and everything works like a charm.
On the iPhone 11, I have also installed the certificate:
And I have enabled full trust for it:
And yet, if I try to visit e.g. https://google.com/ in Safari, I get an error message telling me that "This Connection Is Not Private":
And if I click "view the certificate", it shows that the google.com certificate, issued under the Fiddler root, is "Not Trusted" - with no indication as to why???