Flipping one card doesn’t change the state of the other one. Measuring the state of one of a pair of entangled particles does change the other one & that change appears to be instantaneous. We know this - Aspect carried out the experiment in the early 80s & those results have been confirmed by later, larger scale experiments.
(IIRC It’s possible that a super-deterministic hidden variable system could explain Aspect’s results. But that pretty much requires the universe to deliberately plot against you, which seems very unlikely.)
(IIRC It’s possible that a super-deterministic hidden variable system could explain Aspect’s results. But that pretty much requires the universe to deliberately plot against you, which seems very unlikely.)