[RPG] Does incapacitated condition immunity give immunity to stun

I would say that Alex can no longer finish their turn, as they are immediately Stunned and therefore incapacitated.

Stunned

• A stunned creature is incapacitated (see the condition), can’t move, and can speak only falteringly.

To me, this is no different than if the Monk had attacked normally, without using the Stunning effect, and reduced Alex to 0HP, therefore knocking them unconscious (which incidentally is also incapacitated), which would take effect immediately.

You deal damage

PHB page 194:

Resolve the attack. You make the attack roll. On a hit, you roll damage, unless the particular attack has rules that specify otherwise. Some attacks cause special effects in addition to or instead of damage.

Stunning strike does not say you do not do damage. PHB page 79:

Starting at 5th level, you can interfere with the flow of ki in an opponent's body. When you hit another creature with a melee weapon Attack, you can spend 1 ki point to attempt a stunning strike. The target must succeed on a Constitution saving throw or be Stunned until the end of your next turn.