Do I need an account to use SkipTube?

No. You can watch with no account at all.

Videos with no ads, Home, Search, channels, Subscriptions, Library, captions, the clean player, Focus mode and blocked channels all work signed out.

You need a SkipTube account only to save videos, follow channels, vote, mark a sponsor, get Pro or restore a purchase. SkipTube asks you to sign in at that moment, and says why.