Aren't screenshots just one implementation specific variant of the possible solutions? Recall immediately made me think about a universal API that all kinds of applications write history to. That data can then be searched, or you could possibly even have global undo/redo.

Screenshots are just "easier" to use, because you don't need to implement anything for individual apps. "Easier" only if you have data centers full of compute and the capital to very inefficiently throw a bunch of silicon and electricity at the problem.