My mac pro 2018 can't turn on airplay, how can i fix ?

AirPlay is not meant to work among iOS, iPadOS or macOS devices. AirPlay is designed to work with TVOS (Apple TV) and other devices that have AirPlay capability (Some new televisions).

In short, you will not have the ability to use AirPlay between a Mac and an iPad.

Axel F.

Do you have devices available nearby that are AirPlay capable? Devices such as an Apple TV or an AirPlay enabled Television?

If you do not then the AirPlay Display will only show and remain on OFF.

Axel F.