There are many suggestions already let me through in one more: Affine : https://affine.pro/

You can self host too if you like. Not all features as Notion but comes very close. Seems more private too compared to Notion.

I am also looking for more private and secure Notion alternatives. My company doesn’t allow using Notion.

I like templates, tasks, scrum etc. which I use for personal use. But I am reluctant on saving any personal information in it.