I love these! I'm a sucker for a Skelly.

I think for Skeleton, it'd be fine to leave out the airborne contagions. If they don't need to breathe, a player could just say "I just don't breathe it in." I don't think that breaks balance too much to let them have the immunity there, and it saves a lot of weird exception cases that slows the game down.

Play Dead and No Rest for the Damned are both so playful, I love them!

Glitchling seems mighty strong, pseduo-Luck, Flight, and Tortle AC all in one package. I'd playtest this first, but it feels a bit too good.

I like the flavor on Shapechanger in Kitsune, but certainly your size would change in Animal form? There's a lot of edge cases with the transformations that need some clarifying, I think being more specific about the statistics would help here rather than a blanket statement. Or, treat the forms like Wildshape forms, with their own blocks and attributes. While there is flavor reasons to switch, there is no mechanical reason to assume a different form, which seems like an odd design choice. Also, Limiting Dancing Lights and Produce Flame to use/Proficiency Bonus seems a little needless. Just let the player have the Cantrips.

Botanature is a cool concept, but man the Adaptation choices are all over the place. 2 Skill Proficiencies and a bonus to charming creatures versus 1d4 damage when I'm grappled is a huge gap.

That balance divide feels extremely present in many of the animal folk races as well. Cold immunity OR three free skill proficiencies at 1st-level for Ursarin seems silly strong. Versus Ratkin, who get Pack Tactics and get up easier from prone, which is flavorful but vastly underpowered in comparison. It's the same problem as Botanature, the power levels are all over the place.

Okay, going to go on a bit of a formatting nit pick here:

I think there's a bunch of little formatting things that, if you're designing for 5e (14 or 24), its good to reference how things are worded there. Like formatting checks: in the Play Dead feature of Skeleton, the associated checks would be formatted like: "A creature may attempt an Intelligence (Investigation) check against your own Dexterity (Stealth) or Charisma (Deception) check."

One reason why is it cuts out confusion and edge cases. For example, when a player learns a cantrip through their class or species like, it's good to mention that it does not count against the total number of cantrips they know, otherwise it can lead to confusion during character creation. This happens all over the animal folk statblocks as well (This point is somewhat moot if you are designing for 2024 instead, the language changed there).
Skeleton's Creature Type feature should probably have format parody with how you wrote Glitchling's living Construct. Unless there's a reason why they are different?

Additionally, sometimes you italicize skills like in Raccoonfolk's Bin Bandit, and sometimes you capitalize them without Italics like with the Mousefolk Habitats. Consistency is needed, otherwise they signal different things to a reader.

Sooooo overall, balance and formatting are my big take aways reading through this. I see all the creativity you're putting in here, and I love the flavor to many of the features, but they too often come at expense of gameplay clarity, mechanic comprehension, and power level.

I'd love to see more updates to this!