Default values should not be given in the arguments of __post_init__. They should only be provided as default values for class-level init-only member variables.

from dataclasses import InitVar, dataclass


@dataclass
class C:
    x: InitVar[int] = 1

    def __post_init__(self, x: int = 4) -> None:
        print(x)  # noqa: T201


c = C()  # Prints 1!  4 is ignored.

The above text could be used for the Ruff rule warning message.