Based on this question regarding the interaction of Mounted Combatant and Mobile Feats, there seems to be a possible loophole regarding provoking an OA and being the target of an OA.
Does the redirected attack from Mounted Combatant mean that the mount provokes the OA, but the rider just becomes a target of an attack? Or is the OA and its target always coupled?
First of all, the rules tell us under what conditions you provoke an opportunity attack (OA):
You can make an opportunity attack when a hostile creature that you can see moves out of your reach. To make the opportunity attack, you use your reaction to make one melee attack against the provoking creature.
So, a creature provokes an attack when they move out of your reach. You are then able to choose to target the creature with a melee attack.
Here is the first indication that the two are separate: the creature provokes and then you get to decide if you want to target them. You can ignore the provoke, or you might be unable to act on it (eg you don't have a reaction left). Either way, the provoking comes before and separate from the targeting. Normally, though it doesn't matter since usually a) provoked OA that cannot be acted on are just ignored or b) the creature being targeted by the OA is the one who provoked the OA.
There are some cases where the latter case is not true, for example the case of a mounted rider whose mount has provoked an OA:
if the mount provokes an opportunity attack while you’re on it, the attacker can target you or the mount
Here again is evidence that provoking the OA and targeting with the OA are different. First the mount provokes the OA, then the creature gets to decide which of you it wants to target (or if they don't want to take it).
So, from everything the rules indicates, provoking an OA and being the target of an OA are different things.
