Not really much to go off of here. I feel like I recall some kind of upper class manor/hotel/castle at the start of the movie and some kind of change occurring. Maybe some kind of social revolution or people mutating. I recall an airship with some kind of scientists on board. I think the protagonist was a woman possibly looking for her son.
I say it’s like Fantastic Planet but it might not be fully animated. It could be something a long the lines of human actors with heavy amounts of CG or just very out there sets.
Solved: It was The Congress (2013). A bit harder to find because not all of the movie is animated. The change I mentioned was about 1/3 into the movie after the transition to animation.
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
https://m.youtube.com/watch?v=HLXlHwwDN_4
It was The Congress