First thing that comes to mind is Sky Captain and the World of Tomorrow
https://youtu.be/5D-aYfrthJc?si=7SBWwF8Xq2uxxdLc
Angelina Jolie also starred in another movie called Changeling where she's looking for her son. I wonder if you're combining the two movies together?
It was The Congress. There are airships and people mutating into birds.
I'm glad you found it and I appreciate the update.
Heavy Metal (1981) is often compared to Fantastic Planet. There's no son, but lots of the other things you listed match.
https://en.m.wikipedia.org/wiki/Heavy_Metal_(film)
https://m.youtube.com/watch?v=yKkt_g9Tc7M
https://m.youtube.com/watch?v=T6a3F6fPSP0
https://m.youtube.com/watch?v=dFq0cHHYrSU
Or maybe Heavy Metal 2000 (2000) https://en.m.wikipedia.org/wiki/Heavy_Metal_2000
It was The Congress
Some lesser known movies that come to mind that match the animation style/era;
Delta Space Mission (1984)
The Last Unicorn (1982)
Marco Polo Jr Vs The Red Dragon (1972)
The Son of the Stars (1988)
Rock & Rule (1983)
Time Masters (1982)
American Pop (1981)
Gandahar (1987)
Starchaser: The Legend of Orin (1985)
Fire and Ice (1983)
The Point (1971)
Night on the Galactic Railroad (1985)
The Flight of Dragons (1984)
Wizards (1977)
The Thief and the Cobbler (1993)
Son of the White Mare (1981)
The Spine of Night (2021)
Nova Seed (2016)
A Cat in Paris (2010)
Memories (1995)
Little Nemo: Adventures in Slumberland (1989)
Hope you find what you’re looking for, please let us know if you do!
It was The Congress. I'll have to take a look at some of the movies in your list though
Crowdsource your search for the name of that thing.
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