Why is "not(True) in [False, True]" False?

This is because of the priority of the operator. This is because in has a higher priority than not.

(not True) in [False, True] I think you thought it was handled in the same way as

in reality not (True in [False, True]) Because it's processed in the same way.

Also, not is not a function, so it is not recommended to use it with not().