Sidecar

Sidecar is a feature developed by Apple and introduced as part of macOS Catalina and iPadOS 13.

Usage
Sidecar allows supported Macs (generally 2016 or later) to use supported iPad models as a second monitor. Use of the Apple Pencil is also supported on the iPad models while displaying Mac video.

On a Mac, controls can be accessed through. The preferences can allow the sidebar to be moved to the left or right side of the iPad screen, the Touch Bar to be moved to the bottom or the top of the iPad screen, and double tap to be enabled on the Apple Pencil.

Criticism
Sidecar received some mixed reviews. Sidecar may fail to work after updating to macOS Big Sur. Troubleshooting of plug-ins and iCloud settings may be required to get it to function again.