SkipAds is a viewer for YouTube - a quieter page to watch on. It is not a browser extension, it is not an ad blocker, and it does not change anything about YouTube itself.
Every video on SkipAds plays through YouTube's own player. The video is served by YouTube, counted by YouTube, and governed by YouTube's own player behaviour.
Playing it on a clean page simply carries fewer interruptions than the youtube.com watch page does. That is a property of the player YouTube publishes - not something SkipAds does to it.
Your watch history is kept in your own browser by default. Clear your browser data and it is gone.
Signing in with Google is optional. It exists only so your subscription feed and playlists can follow you between devices - the parts of YouTube that need to know who you are. You can use everything else without it.
Some creators do not allow their videos to play outside YouTube, and those cannot play here - that is their choice and SkipAds respects it. Age-restricted and region-locked videos may also be unavailable.
SkipAds is a viewer, not a replacement for YouTube. Posting comments, liking and subscribing all still happen on YouTube itself.
SkipAds is free and has no ads of its own. If it is useful to you, you can buy me a coffee.