No adventures have come out since last week.
I mentioned Witchlight and Mordenkainen Presents: Monsters of the Multiverse -- the books that changed the monsters from just spells -- and then asked about adventures since. I am unsure how you got last week.
Magic Action is casting spells, activating magic items, ect... so any of those things in the adventures would count as one.
Yes, and there are cases it isn't clear and the DM needs to make an ad hoc call.
Looking at some of the Duergar from MP:MotM:
Mind Mastery. The duergar targets one creature it can see within 60 feet of it. The target must succeed on a DC 12 Intelligence saving throw, or the duergar causes it to use its reaction, if available, either to make one weapon attack against another creature the duergar can see or to move up to 10 feet in a direction of the duergar's choice. Creatures that can't be charmed are immune to this effect.
Soulblade.
Melee Spell Attack: +5 to hit, reach 5 ft., one target.
Hit: 10 (2d6 + 3) force damage, or 13 (3d6 + 3) force damage while under the effect of Enlarge.
These are both psionic effects. According to your definition, the first is not a Magic action. Is the second because it says spell attack? Either way you answer it causes issues - there are a lot of things that aren't listed as spells except for Spell Attack that as DM I would rule as Magic actions, but if you use that then some psionics is magic and some is not - and the one marked spell attack is very similar to things like the Soulknife's power, which is not a spell. Unless you say they are both Magic actions, in which case the first is definitely outside your definition and again proves my point from a different direction.
It's not as simplistic as you say.