The https://mantine.dev docs rule. They provide a lot of examples on the landing page and if you navigate through the page each component has a great explainer with a playground and all possible settings you can give. Direct with links to the source code and a great CMD+K search.

https://supabase.com/ is very clean with a nice information hierarchy.

https://www.postgresql.org/ despite being quite technical, these docs are very easy to follow in a self learning format.

The new Angular and React docs are quite nice.

https://zulip.com/