writable-keys

WritableKeys<Type> constructs a union type by picking all writable properties of object type Type

interface UserThatCannotChangeEmail {
  id: number;
  readonly email: string;
  name: string;
}

type PropertiesThatUserCanChange = WritableKeys<UserThatCannotChangeEmail>;
//   ^? 'id' | 'name'

It means properties which values can be reassigned

declare const user: UserThatCannotChangeEmail;

user.id = 1;
user.name = "Alex";

TS Playground – https://tsplay.dev/NV3XGm