That feature was available and only possible with specific Intel chips. It went away because Intel stopped supporting it. Sad the feature didn't come back to life in the AppleSilicon iMac.

Their display stack on Apple Silicon is still maturing. It took way too long for them to support more than a single external display. I bet you it's due for a comeback in the next decade.

My father-in-law just replaced his daily iMac because _Chrome_ finally stopped providing security updates for part of his hardware architecture.