Arguably, this isn't your problem. In most circumstances, you don't give loot to specific characters - you give it to the party, and let them sort out how it gets distributed.
Yes, this could theoretically lead to one player hogging all the magic items, but that's a solved problem; As long as your players are aware that they can negotiate how stuff gets shared around, they'll generally spot unfair situations, renegotiate as necessary, and generally agree on equitable solutions on their own.
If one player's lack of magic items is dragging the party down, that's the whole party's problem, and most players will realise that pretty quickly; Even the most selfish of players will agree it's a good idea to share the wealth if it improves their own survivability.
If magic items have already made one player much more powerful than the others - Well, it's not like magic items are bound to the first person who picks them up; Your players can always just redistribute them where they'll be more useful.
If your players don't find an uneven distribution of loot to be inequitable - Well, then there's no problem to solve; Everyone's already having fun, and that's what the game is all about.
So, to repeat myself, this isn't your problem: Working out how to distribute loot is just another part of the game. Heck, some players find it one of the most fun parts of the game: Working out how to effectively use available resources is core gameplay, and deciding how magic items should be distributed for best effect is part of that.
I would say that Alex can no longer finish their turn, as they are immediately Stunned and therefore incapacitated.
- 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.
5 spells, the Monk's Stunning Strike, and a few items.
The only ways, disregarding items, to stun a creature are the Monk's Stunning Strike (PHB):
The Contagion (PHB) spell:
The Divine Word (PHB) spell:
The Psychic Scream (XGtE, 163) spell:
The PW: Stun (PHB) spell:
The Symbol (PHB) spell:
Including items, the DMG lists the Legendary Hammer of Thunderbolts, the very rare Robe of Scintillating Colors, the very rare Staff of Thunder and Lightning, the rare Wand of Wonder (only stuns you, though), and the legendary Whelm.
The Princes of the Apocalypse book also has an uncommon Storm Boomerang that stuns (credit to NautArch for finding this):