I want to suggest you to port outline for Linux.
1. There are almost no competion for similar notetaking software on linux.
Linux don't have any notetaking/journaling applications comparable in quality and functionality to Onenote/Outline.
2. There is demand for it.
For example I saw multiple posts in different parts of the internet of people who want to migrate to linux, but can't because it doesn't have anything similar to onenote.
My thinking is that it shouldn't be hard to port Outline to Linux, I might be wrong
Could you seriously consider doing that?