You can use set and set comprehension:
{hobby for name, hobbies in input.items() for hobby in hobbies}
As m.wasowski mentioned, we don’t use the name here, so we can use item.values() instead:
{hobby for hobbies in input.values() for hobby in hobbies}
If you really need a list as the result, you can do this (but notice that usually you can work with sets without any problem):
list({hobby for hobbies in input.values() for hobby in hobbies})