Projectors: mirroring and extending displays on a mac
https://support.apple.com/guide/mac-help/extend-mirror-mac-desktop-multiple-displays-mchlb5f905a1/mac
On your Mac, choose Apple menu
> System Settings, then click Displays
in the sidebar. (You may need to scroll down.)
From here, you can modify the resolution and add extended displays.
To add a display, click the + pick the room you want and choose whether or extend or mirror. If the resolution is too big, you'll want to make your text larger by selecting the various resolutions under built-in display.