I’m on an unlimited PTO policy. Do I formally quit or just disappear until they fire me?

Edit: Been getting some hate so maybe some added context might help. Our official PTO policy is unlimited, however like any other PTO, it has to be approved by your boss. Well my boss decided I had taken enough PTO per his own personal philosophy that wasn’t ever shared, and denied my family vacation. So, that at that point, it’s no longer unlimited in practice.