I AirPlay’d my display to a second computer/monitor during IWC Online 2019, and it was great. Even better during a video chat is controlling the second computer with my primary mouse and keyboard. My go to used to be Synergy, but they went paid without convincing me they were doing anything interesting. Since its GPL, its been forked, and was easy to install https://github.com/debauchee/barrier.πŸ‘
GarageBand is missing shortcut for Delete and Move.

System Preferences -> Keyboard -> Shortcuts -> App Shortcuts
Press + button, select GarageBand.app
type Delete and Move, and assign it a key
I stole CMD-D from New Track with Duplicate Settings