Sidecar in macOS turns your iPad into a second display, but it's limited to certain Macs and iPads. Thankfully, a few ...

How to use an iPad as a second screen for your Mac The ability to use an iPad as an extra display is built into macOS and iPadOS, and it works completely wirelessly.

Here is a quick hands on and tutorial on how to turn your iPad into the best portable display for any device.