daisy chain two iMacs

De[ends...

You can connect any of these older iMac models to another Mac from 2019 or earlier for use as an external display. Learn how to identify your iMac model.

• 27-inch iMac models introduced in 2009 and 2010: Use a Mini DisplayPort cable to connect your iMac to a Mini DisplayPort or Thunderbolt or Thunderbolt 2 port on the other Mac.
• All iMac models introduced in 2011, 2012, 2013, and mid 2014: Use a Thunderbolt cable to connect your iMac to a Thunderbolt or Thunderbolt 2 port on the other Mac. If the other Mac uses Thunderbolt 3, you can use the Apple Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter with your cable.

Target display mode requires macOS High Sierra or earlier on the iMac used as the external display. It does not work with macOS Mojave or later.

Only if they meet the requirements in this Apple document: Use your iMac as a display with target display mode - Apple Support

The 2020 iMac can't use a Thunderbolt iMac as a display, but despite what Apple says, can use use a 27" 2009 or 2010 iMac. It will need a USB-C to Mini DisplayPort cable, such as:

mophie USB-C Cable with Mini DisplayPort Connector - Apple