As far as i know, they don’t use the youtube api. Therefore they don’t have to be compilant with any api policy or tos. They just connect to YouTube like any browser do and then show that information(with modifications) on the invidious app.

Google can try to modify the code faster than the developers try to update the app since they expect the data to be in an specific format, but that’s all, they aren’t using the api… There is nothing to be closed.