Critical miss just means you rolled a 1 on your d20, and doesn't have any other consequence. It's just to let you know that you rolled a 1 and would miss regardless of AC or hit bonus.
This. A roll of a 1 is always a miss, no matter what.
Unlike skill checks where you can actually still manage the check with a roll of a 1 if your modifiers are high enough.
In combat a roll of a 1 is always a miss, no if's or but's.
That means unless you have some reason for your hit to automatically hit, you can actually not have 100% chance to hit with an attack. Even with advantage against a monster with AC of 0 you have a 0,25% chance of missing out right. Without advantage you will only have a 95% chance of hitting any monster regardless of AC and attack modifiers.
So there is a difference between miss and critical miss in that sense.
