1. There used to be an option for fixed or evergreen exports, it seems like it's only evergreen now, why is that?
Fixed mode is still supported. It's covered in the Exporting to Windows with the WebView2 wrapper tutorial. I would recommend the latest version though - fears of breakage are usually over-done, as Construct's web exports have been working reliably for years, and even if something breaks, you can always patch your game.
2. If I use either types of export, I assume there still can be future updates to the exe and dll provided with the export on C3 side, how do I track if and when a new version of that is released?
Just keep an eye on the changelogs of releases - any such changes will be noted.
3. Possibility of controlling the data folder name? -> see this post:
https://www.construct.net/en/forum/construct-3/how-do-i-8/control-name-data-directory-180023
I don't see any reason why this needs to be changed.
4. In theory will it be possible to run C3 editor with it as we used to do with NWjs?
No, we plan to keep Construct running in the browser. The NW.js editor had a bunch of bugs and limitations due to not being a real browser, and it really has negligible benefit these days anyway, as you can do things like use project folders directly in the browser now (which was one of the main original motivations for having a desktop download).