There is a core setting which states the following:
allowframeemedding - If enabled, this site may be embedded in a frame in a remote system, as recommended when using the 'Publish as LTI tool' enrolment plugin. Otherwise, it is recommended to leave frame embedding disabled for security reasons. Please note that for the mobile app this setting is ignored and frame embedding is always allowed.

If the description was true, h5p content should work with this disabled, for the mobile app. However h5p does not work for this, and there seems to be no clear reason why this is the case.

Other mentions I've found so far:

https://docs.moodle.org/37/en/Interactive_Content_-_H5P_activity#Moodle_Mobile_App_compatibility

Note 1.- The help text in this 2nd parameter displays a wrong piece of information. It reads "Please, note also that for the mobile app this setting is ignored and frame embedding is always allowed." This is not true for H5P, Frame embedding must be enabled. 

https://docs.moodle.org/311/en/Moodle_app_FAQ

H5P packages are not working on iOS

This is caused by a new feature of iOS 14 called ITP that blocks cookies for external sites embedded in the app (the H5P content is played embedded in an iframe pointing to the Moodle website) unless the user enables a setting in the app to allow those cookies.

The quick workaround is to ask your students using iPhone/iPad with iOS 14 to enable the setting "Allow Cross-Website Tracking" available via the Settings app (look for the Moodle app, at the bottom) 

I have found the line which performs the check and will push a PR through, but if the PR is rejected it should still be clear in the code why it cannot be supported in this regard.