How would this sentence “important display message” vanish?

To my knowledge, you can't delete that message from Settings>General>About...

See this support article (at section "Important Display Message", last paraghraph):--> About genuine iPhone displays - Apple Support

For any further question about that, contact Apple Support directly, using this link:--> Get Support , or make an appointment and have your device inspected at an Apple Store or AASP (Apple Authorized Service Provider) among this list:--> Apple – Location Selector

Regards

Giulio

What that message means, and for how long and where it’ll be shown ➡️ About genuine iPhone displays - Apple Support