Tried enabling iMessage Contact Key Verification and got this extremely helpful error. For clarity, that is a list of all my Apple devices with iMessage.
I tried initiating the process on all three devices and always get the same error, so I don’t know what “Apple ID Settings” I’m supposed to update. I’ve updated the second Macbook to 14.2.1 by now and retried – no dice. Based on the requirements listed on the linked page, I don’t see why it doesn’t work, so specifying which device is causing an issue and why/what exactly would be helpful.

Under “If iMessage Contact Key Verification isn’t working” there’s a link to another support page, but it’s only about problems after already enabling it.