You can pretty easily see all the traffic on your own phone. You can even do it on device
If this app works without root, it must be possible to apps on iPhone to add their own certificates to the system, which are then trusted by other applications - that would already be pretty alarming. I think Android still requires certificates to be manually imported by the user. Maybe this app points you to instructions on how to do this, but the description makes it sound very automatic.
https://andydavies.me/blog/2019/12/12/capturing-and-decrypti...