Mypy reports no error for this program:

from typing import ReadOnly, TypedDict, NotRequired

class TD(TypedDict):
    x: ReadOnly[NotRequired[int]]
    
def f(td: TD):
    td.pop("x")

https://mypy-play.net/?mypy=latest&python=3.13&gist=9dfad53c9dc2e22c63548a553afdb67e

But deleting a ReadOnly key should not be allowed. The spec says:

The typing.ReadOnly type qualifier is used to indicate that an item declared in a TypedDict definition may not be mutated (added, modified, or removed)