Found a post of the monsters by CR
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The Celestial stuff is the most interesting to me. Interestingly the natives of the Outlands appear to be Celestials which seem to have become the default for creatures of the Outer planes and Astral were Aberrant, Contruct, and Fiend don't make sense even if they aren't particularly linked to an Upper Plane. Dabus, Sunflies, and Rilmani are both Celestials, which means they can be targeted by spells and effects that target Celestials.
Archons and Guardinals get 3 apiece suggesting the rest could be in the 2024 MM and/or D&D Beyond Compendium.
Barbiurs are also Celestials, that could be why no playable version. Not sure why that would be worse then playable Fey, Monsterousity, or Ooze. Also possibly the only Chaotic Good Celestial, with the rest being Lawful Good, Neutral Good, True Neutral (or perhaps varied in the case of Sunflies). Not sure about the Celestial Planar Incarnate (could these be different to the Incarnate from past editions of Planescape, I mean those were simply known as Incarnates, not Planar Incarnates, CR22 seems high for OG Incarnate).
For fiends a couple of Yugoloths, Demodands, Malephants, a Reflection, with the most powerful being the Fiendish Planar Incarnate.
Celestial Eladarin seem completely left in the cold, also no Lillend or Asuras, with Aborea getting the short end of the stick, as while Aborea does have a Barbiur they are simply immigrants from Ysgard.
Githzerai Aberrants are weird given Gith hate Aberrants, especially Mindflayers. But could it be linked to becoming more linked to Limbo whose main creature type appears to be Aberrants like Slaads? Could these be more Chaotic Githzerai, a kind of substitute Limbo Planar race to Slaads who suck at being Chaotic Neutral Paragons?