The High Aldwin
We discussed this a bit before.Again, I'd just use a strict reading of the ruling in the Sage Advice Compendium. Otherwise, if you just try to use common sense about what feels "magical," Vecna can just collapse into a pile of bones.
• Is it a magic item?
• Is it a spell? Or does it let you create the effects of a spell that’s mentioned in its description?
• Is it a spell attack?
• Is it fueled by the use of spell slots?
• Does its description say it’s magical?
For me, only IDS doesn't fit any of those. Divine Smite fails to "fueled by spell slots" and Ki-Empowered Strikes says "... your unarmed strikes count as magical ..." so fails the last criteria.
So, what is your take?
Also, as far as I can see, I think Malek will have to break out a torch and start burning Vecna... I don't think he has other options.