Screen share from Macbook to old Mac

The host machine, sharing the screen can also share its screen through Apple menu -> System Preferences -> Sharing -> Screen Sharing.

As long as the Macs are on the same network, or a Mac is on a predefined static internet IP (192.x.x.x and 10.x.x.x are both specific to in house routers and WiFi/Airport stations are harder to screen share over the internet), you can share with another Mac, your screen, if you know its user's login credentials that are sharing the screen. The client machine System -> Library -> CoreServices -> Applications - >Screen Sharing can open and connect to the address specified on the Sharing System Preference panel. Typically you can also on the Finder's Go menu -> Connect to Server connect to VNC://IP address remote to the machine in question.

While slower than target display mode mentioned by Todd, it also offers drag and drop file transfer from one machine to the next.

Greetings KateMooreDesigns,

You've come to a great place for help! To confirm, is the Mac you're wanting to use as a second display an iMac? If so, you'll want to make sure your Mac meets the system requirements outlined below. You can also view these system requirements in the following article. The article also outlines what cables are supported to connect the Macs.

The following older iMac models can be used as an external display when plugged into another older Mac model.

"iMac models introduced in 2011, 2012, 2013, and mid 2014"

"To use any of these iMac models as an external display:"

• "The iMac used as a display must have macOS High Sierra or earlier installed.
• The other Mac that you're connecting it to must have been introduced in 2019 or earlier and have macOS Catalina or earlier installed.
• The cable connecting the two Mac computers must be a Thunderbolt  or Thunderbolt 2  cable."

"24-inch and 27-inch iMac models introduced in 2009 and 2010"

"To use any of these iMac models as an external display:

• The iMac used as a display must have macOS High Sierra or earlier installed.
• The other Mac that you're connecting it to must have been introduced in 2019 or earlier and have macOS Catalina or earlier installed.
• The cable connecting the two Mac computers must be a Mini DisplayPort  cable."

Use your iMac as a display with target display mode

You can also find more information about using external displays with your Macs via the article below.

Connect a display to your Mac

Take care!