Jailbreaking an iPhone and using a tool like SSL Kill Switch [1] or just plain, old Frida with a script like [2] will do the job. Jailbreaking is the hard part, especially for an up to date iPhone, after that there's loads of guides you can follow that disable certificate validation for pretty much every application. It all boils down to hooking the necessary validation functions and having the APIs lie to the app code.

Some apps package their own crypto helpers (often with big crypto problems) to make this harder and require actual reverse engineering, but those are a pain to maintain and it's only a matter of time before someone finds a way around them. If you can extract the symbols (so if the app has not been obfuscated well) you can use Frida's API to hook those as well through any language you like. There's even an interactive Javascript console you can hook into the apps you're hooking!

Certificate pinning is a great way to protect users' security and privacy, especially in countries with questionable governments or ISPs, but it won't protect your app's secrets.

[1]: https://github.com/nabla-c0d3/ssl-kill-switch2 [2]: https://techblog.mediaservice.net/2020/08/ios-13-certificate...