Can the Grave cleric's Sentinel at Death's Door feature turn a critical hit into a miss, while adamantine armor does not?

Question

I have asked a question before about this Grave Cleric feature in the past, and was inclined to believe that you are able to turn critical hits into misses by way of the feature, but upon looking into it further, I found that adamantine still gets hit as in this question.

I have also found questions, like this, where it says Sentinel at Death's Door does not work on crits.

Is Sentinel at Death's Door able to cancel a critical hit into a normal hit and potentially a miss, and adamantine cannot? Or can neither do that?

Answer 1

Both Sentinel at Death's Door and adamantine armor turn crits into regular hits

The Grave Domain cleric's Sentinel at Death's Door feature (XGtE, p. 20) says:

At 6th level, you gain the ability to impede death’s progress. As a reaction when you or a creature you can see within 30 feet of you suffers a critical hit, you can turn that hit into a normal hit. Any effects triggered by a critical hit are canceled.

The description of the magic item adamantine armor (DMG, p. 150) says:

This suit of armor is reinforced with adamantine, one of the hardest substances in existence. While you're wearing it, any critical hit against you becomes a normal hit.

Both the Grave cleric feature and the magic armor say that the critical hit becomes a normal hit - but it's still a hit. Given this wording, any modifiers to the roll or the target's AC do not change the fact that it remains a hit, because it explicitly says the attack becomes a "normal hit" but not that it needs to beat the target's AC.