My screen recording function is disabled and I don’t know how to turn it on

Start reading this support article:--> Edit Control Center on your iPhone, iPad, and iPod touch, then add Screen Recording option (if missing in your Control Center).

Check also:

Settings>ScreenTime>Content&Privacy Restrictions>Contents Restrictions>Game Center>Screen Recording... must be set to "allow". When done, restart your iPhone.

Regards

Giulio