Notesnook for sure. I really disliked Joplin. Particularly the Android app. Just really poorly designed.
Acreom promise but it’s new enough they don’t have E2EE or even local only on mobile. Both are on the road map. Dev seems engaged and cool though.
Edit: I didn’t see the open source req, acreom isn’t. But it’s still a cool app. And I’d they can get local only on mobile, then you can sync however you want as it’s just flat Markdown, similar to Obsidian.