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You can, on a rooted phone. There's ways to install a CA certificate with root (described in my only popular blog post) but there's also alternatives, like using Frida to disable TLS verification all together.

It's certainly not as easy and reliable as it used to be, but it's still common for security research to use these tactics to see what apps are doing.

The basis of many enterprise networks is device-installed CAs so I would be thoroughly surprised. iOS at least still allows you to install a custom CA and only a few apps will refuse to work with it, who likely reject connections that aren't secured via a specific CA.

From a legitimate reverse engineering/security auditing standpoint, cert pinning is generally very trivial to bypass.

see: Frida, xposed framework (not sure if still relevant)

There is a way to do it where you recompile the APK to enable trusting user CAs, see https://daksh.github.io/MITM/.