Example for SO question: https://stackoverflow.com/questions/74914319/how-to-type-only-the-first-positional-parameter-of-a-protocol-method-and-let-the/75002538#75002538

my_protocol.py

T = TypeVar("T")
class MyProtocol(Protocol[T]):
    def my_method(self, first_param: int, args: T) -> int:
        ...
@dataclass
class Imp1Args:
    x: float
    y: float

class Imp1(MyProtocol[Imp1Args]):
    def my_method(self, first_param: int, args: Imp1Args) -> int:
        return int(args.x + args.y)