https://freetubeapp.io/

https://github.com/FreeTubeApp/FreeTube

Not 100% sure it supports login, but it does support this, which is like 90% of the way there:

> Import Subscriptions

> Import your subscriptions from YouTube to see your feed instantly

Freetube doesn't support logins. It also breaks every now and then as Youtube does their thing, but the devs are usually pretty ontop of it.