Undocumented and 'illegal' use of $CFG->disablemobileappsubscription

This setting is:

1. not documented, anywhere
2. not set anywhere
3. not positive

All settings must be documented, and all settings must use positive variable names. Always.

https://docs.moodle.org/dev/Coding_style#Variables

Use positive variables names always (allow, enable not prevent, disable).