After 6 weeks at Level 43, I’ve finally moved onto Level 44. I’m making good progress at collecting a 3* living form dex also. I have noted all the missing Pokémon forms at 3* (excluding costumes, lucky and shadow Pokémon) for the first five gens, including those unreleased. Currently, Kanto is missing 8, Johto is missing 35 (lots of Unown), Hoenn is missing 18, Sinnoh is missing 52 (lots of Arceus, Rotom forms and some unreleased Pokémon), and Unova is missing 43. For Kalos, every form I obtained, I have in 3*. For Galar, all except Mr. Rime. It will be interesting to see how much these numbers will be reduced by the next level.
I am missing 22 from the current Pokédex, as well as 53 from the current 3 Stars filtered Pokédex.