connecting iMac mid 2014 to new iMac as an external display

It may not work since your new Mac , that is Mac that you're connecting it to must have been introduced in 2019 or earlier and have macOS Catalina or earlier installed.

This:

Use your iMac as a display with target display mode - Apple SupportIncludes:

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.

Monterey on the new iMac is not an issue.

Your old iMac must be running 10.13.6 at most.

If it is running Mojave or later, then you will need to install High Sierra.

You will of course also need the Apple Thunderbolt3-Thunderbolt2 adapter, and a Thunderbolt2 cable.

As long as the old mac supports Target Display Mode, it will work - and that is where the system installed in that old mac is crucial.

omri_apple wrote:

Thanks guys. This is so irritating. Apple making sure that all their old product is redundant further increasing the electronic waste. What can one do with the old tech??

I think it is a business decision. The extra expense of making these things compatible as the operating system advances was probably evaluated as not a good return on investment because the number of customers wanting to do this is probably very small. External displays are also pretty cheap nowadays anyway.

Please see lllass post! - I was WRONG.

Only macs released in 2019 or earlier can use another imac as a target display - so M1 macs are out.

Thank you, lllass - I stand corrected.