$ cat >ruf033.py <<'# EOF'
from annotationlib import get_annotations
from dataclasses import dataclass
@dataclass
class C:
    def __post_init__[T: (str, bytes)](self, a: T | None = None, b: T | None = None) -> None:
        self.a = str(a)
        self.b = str(b)
print(get_annotations(C))
# EOF

$ python3.14 ruf033.py
{}

$ ruff --isolated check ruf033.py --select RUF033 --unsafe-fixes --fix
Found 2 errors (2 fixed, 0 remaining).

$ cat ruf033.py
from annotationlib import get_annotations
from dataclasses import dataclass, InitVar
@dataclass
class C:
    a: InitVar[T | None] = None
    b: InitVar[T | None] = None
    def __post_init__[T: (str, bytes)](self, a: T | None, b: T | None) -> None:
        self.a = a
        self.b = b
print(get_annotations(C))

$ python3.14 ruf033.py 2>&1 | tail -n 1
NameError: name 'T' is not defined