Apple has started distributing macOS Monterey as a free update to most Macs that have been around since 2015. After the update, you can use an iPad as a second display without prior setup, among other changes.
https://www.notebookcheck.net/Apple-releases-macOS-12-Monterey-with-AirPlay-on-Mac-live-text-and-bokeh-for-video-chats.575302.0.html