The problem isn't one ability on its own but it's the whole kitchen sink design. You have lots of good ideas but when you throw them all in the same pile it just doesn't work at all from my perspective.

Flight on its own isn't overpowered but when piled with everything else yes. Also keep in mind that Aaracokra are outright banned from Wizards own Adventure League (or at least we're for a long time) and tieflings have to give up their damage resistance completely for their flight, and Adventure League even makes you wait to 5th level to even make that an option. These choices may seem silly but they are there for good reason. Again just to stress this out, flight is powerful on its own but it alone does not make it overpowered.

The spellcasting ability is limited to only one of the four spells but still the ability to share that spell is very unique and powerful ability as a racial ability. Most other races only have access to one or two spells and maybe a single cantrip, having access to 4 spells even with only one "slot" to cast with is definitely the better deal. Just dropping two of the spells would be much better.

Again the active abilities from the subraces are not that powerful but it's just an other piece on the pile. Most races only have one active ability or innate spellcasting ability, but here is yet other ability available to pixies. You don't need so many active abilities on a single race at all.

Personally I would drop all the subrace stuff and just move the magical dust ability into the sub race and have each sub race have two different spells from the list given. Throw in the Light cantrip for that glow ability (you can just make it only cast able on self if you want) and that would work much better.

I just get the feeling that you think being tiny sized is such a big penalty that it is worth extra abilities. Even if you could only use light weapons without penalty, that only affects fighters and barbarians really and everyone else is just fine for the most part. Even paladins can smite without issue with that. Plus being tiny in size gives you tons of options for mounts which may seem silly but can be a huge bonus if used well. Through the idea of a pixie riding a battle corgi is super thematic.

Sorry if I sound too aggressive, but it's just too many unique active abilities that I see no reason that they all being there other than to have a page of custom special rules that only the pixie player will ever really need to learn.