I know from the question "Does a natural 20 on the attack roll still automatically hit if the target is wearing adamantine armor?" that a critical hit against adamantine armor will still hit, but I was curious whether it no longer being a critical hit affects features or feats that are dependent on a critical hit.
An example: Recently, in a kind of PvP session, I was wearing adamantine armor (plate), and my friend had the Great Weapon Master feat. The first benefit of the Great Weapon Master feat is listed as (PHB, p. 167):
On your turn, when you score a critical hit with a melee weapon or reduce a creature to 0 hit points with one, you can make one melee weapon attack as a bonus action.
Would a critical hit that became a normal hit still activate the bonus action melee weapon attack?
The wording of the Great Weapon Master feat is tripping me up in this case. If a player "scores" a critical hit, is that something that should affect them even if the hit ends up as a normal hit?
For the record, my view on it is that the effect wouldn't work because it ends up not being a critical hit. However, both the other player and the DM in the example I give ruled otherwise, so I'm just seeking confirmation to show them in case the situation comes up again, not trying to argue against what I believe is an obvious ruling.