I'd say Affine or Obsidian.

Obsidian is built on-top of just markdown files, so you can do whatever you want with them. E.g. if you need multiplayer editing you could use 3rd party solutions or even something like HedgeDoc.

Affine is more closer to Notion and self-hostable.

Obsidian: https://obsidian.md/

Affine: https://affine.pro/