iMac as monitor

Hi dagger33,

To see details on Target Display Mode, see: Use your iMac as a display with target display mode - Apple Support.

(Please Note, the iMac MUST be running macOS High Sierra (10.13) or earlier for this to work. For example, if the iMac is on Mojave, it will not work!)

(If the iMac is on High Sierra (10.13) or earlier): You will need: Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter - Apple and https://www.apple.com/shop/product/MD861LL/A/apple-thunderbolt-cable-20-m.

Cheers,

Jack

In addition, the MacBook Pro must be running Catalina or older. There are plenty of reports of Big Sur breaking TDM on computers where TDM worked fine running Catalina.