from typing_extensions import Generic, Protocol, TypeVar
T1 = TypeVar("T1")
T2 = TypeVar("T2", default=object)
class A(Protocol[T1]): ...
class B1(A[T2], Protocol, Generic[T1, T2]): ... # the workaround
class B2(A[T2], Protocol[T1, T2]): ... # the problem
B1[str] # ok
B2[str] # TypeError

Traceback (most recent call last):
 File "/home/joren/huh.py", line 11, in <module>
 B2[str] # TypeError
 ~~^^^^^
 File "/home/joren/.pyenv/versions/3.12.11/lib/python3.12/typing.py", line 398, in inner
 return func(*args, **kwds)
 ^^^^^^^^^^^^^^^^^^^
 File "/home/joren/.pyenv/versions/3.12.11/lib/python3.12/typing.py", line 1110, in _generic_class_getitem
 _check_generic(cls, params, len(cls.__parameters__))
 File "/home/joren/.pyenv/versions/3.12.11/lib/python3.12/site-packages/typing_extensions.py", line 3085, in _check_generic
 raise TypeError(f"Too {'many' if alen > elen else 'few'} arguments"
TypeError: Too few arguments for <class '__main__.B2'>; actual 1, expected at least 1

Traceback (most recent call last):
 File "/home/joren/huh.py", line 11, in <module>
 B2[str] # TypeError
 File "/home/joren/.pyenv/versions/3.9.23/lib/python3.9/typing.py", line 277, in inner
 return func(*args, **kwds)
 File "/home/joren/.pyenv/versions/3.9.23/lib/python3.9/typing.py", line 1004, in __class_getitem__
 _check_generic(cls, params, len(cls.__parameters__))
 File "/home/joren/.pyenv/versions/3.9.23/lib/python3.9/site-packages/typing_extensions.py", line 3049, in _check_generic
 raise TypeError(f"Too {'many' if alen > elen else 'few'}{things}"
TypeError: Too few parameters for <class '__main__.B2'>; actual 1, expected at least 1