Using mac mini

If your Mac and iPad meet the requirements, you can use the iPad as a second display for the Mac Mini, with the aid of Sidecar. You can't use the iPad as your only / first display.

Use an iPad as a second display for a Mac - Apple Support

You can also use AirPlay to Mac to stream iPad video to your Mac, or to mirror the iPad's screen on your Mac.

Use AirPlay to stream video or mirror the screen of your iPhone or iPad - Apple Support

The Mac mini is a desktop computer that runs macOS. To use the Mac mini, you need to connect an external monitor, keyboard and mouse to it.

An iPad run iOS. It is a hand held device similar to an iPhone.