The new content needs to be enabled via experimental data packs.
Go to Create New World > Data Packs.
Click on the "bundle" and "update_1_20" data packs.
Click "Done".
After reading the warning, click on "Proceed".
Click "Create New World".
Maybe you didn't turn on the datapacks?
Resolved, next time I'll be more careful when creating a ticket
When creating the world, you need to turn on the built-in data pack and then the mobs will be available
I just wanted to write about it