I don't believe this exists currently, unless this was added with version 12 (I haven't been able to upgrade yet). I haven't seen it in version 11.0.2311.50556, nor do I remember seeing it in the previews of version 12.
It would be a nice addition to Field Rules in forms if we could set a rule based on a field being changed.
Example: Make Field B required when Field A has been changed.
or
Example: Show Field B only after Field A has been changed.
We can do this now with Javascript and a third field. Example: When Field A changes, populate a value into Field C, and have a field rule that controls Field B based on the value in Field C. But it would be a cool addition to be able to do this via Field Rules without the need for the third field or Javascript.
Even better would be if it could identify changes by the user versus changes by the system (i.e. lookups) so that you could make sure a lookup didn't trigger the field rule by populating the trigger field, but a user could do it.