Word for when two people type the same thing at the same time in chat

If it were spoken word, one would yell "Jinx!" (Alternately, "Jinx, buy me a coke!")

And, according to the rules of the game when I grew up, be unable to speak until they purchased a Coke for the yeller. If they spoke prior to paying the fine, they were subjected to a hard punch in the upper arm.

As to its use in chat . . . Well, I think it could be applicable.

In radio comms this is 'crosstalk' and could apply to text as well. Crosstalk can mean several related things, but generally means interference between channels or between halves of a half-duplex channel.

The dictionary definition isn't as specific as its use in radio jargon.

it is called synchronicity. when two people come up with something at the exact same time.