I don't think it should. There are two better options:

1. Pass in ParamListBase, $Keys<ParamListBase> as params here
2. Probably better: set these as default params in LinkTo, so no changes would be necessary on this line:

declare export type LinkTo<
  ParamList: ParamListBase = ParamListBase,
  RouteName: $Keys<ParamList> = $Keys<ParamList>,
> =
  | string
  | {| +screen: RouteName, +params?: $ElementType<ParamList, RouteName> |};