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 enable the setting "Allow Cross-Website Tracking" available via the Settings app (look for the Moodle app, at the bottom) on your iPhone/iPad with iOS 14.