Unfortunately, GitHub does not provide that granularity for developers. That is way you have an alternative option as general Git provider where you can use fine-grained access token.

You need only "Contents" Read and write permissions. Make sure when you generate fine-grained personal access tokens on the following page: https://github.com/settings/personal-access-tokens/new you select your desired repo (because it defaults to public repos and that will not work).

No

Any plan to have one?

I don't rely on any external framework like Capacitor to make hybrid apps, all of the bridging between web and native part is done by myself.

Thank you for types reporting, fixed all of them. Regarding self-hosted Gitlab, you can already use it with generic Git notebook provider.

NotesHub has support of Mermaid diagrams that has mind-mapping. Or you can use Whiteboarding functionality to mimic mind-maps.

If you are talking about Linux, you can use the Web version, which is Progressive Web Application, works offline and can be installed.

It's not a Flutter app. It's a React-based app.

It's not open sourced. You can look at Settings -> Third-party Licenses to see what libraries are in use.

The web version is free, native versions have small one-time fee.