Checking Optional variables against None would be more explicit.

A part of the Zen of Python is implicit is better than implicit. Compare these two functions:

from typing import Optional

def foo(value: Optional[str] = None):
    if value:
        ...
def bar(value: Optional[str] = None):
    if value is not None:
        ...

Which more explicitly communicates the intent of the code to the developer reading it? Which is more permissive of unexpected falsey inputs were passed inadvertently passed to the function?

Testing an object's truthiness via if value evaluates to True if value.__bool__() returns True or if value.__len__() returns an integer other than 0, or if value is neither None or False. That's a lot of things a developer must to consider when building a mental model of the code.

On the other hand, explicitly checking if value is not None removes those branches of thought entirely from the mental model a developer has to build when reading and understanding the code.