It doesn’t quite fit your requirements, but org mode from emacs is very close.

.org files instead of .md, and the preview does require a bit of config, but it’s not as bad as some make it be, especially if you pickup a preconfigured emacs “distro” (like doom emacs for example) in which case I think it’s just a feature flag to set to on.

Org is also very appreciated for it’s TODO features, which you seem to make a big use of.

It probably isn’t a match for you due to the markdown requirement, but I’m mentioning it just in case you didn’t consider it in the past.

Character is Daniel Jackson from Stargate SG-1

Except probably her: https://youtu.be/tPp-U4QonnM?si=8DJDsvgObkXejitj

( has no link to star trek, but it poped in my head because of the title , and it think it’s funny )

As others have mentionned downloading the .deb and running it will also work, but I feel nobody gave your a tldr of why you may want to follow those instructions instead, so here it is:

Those instructions configure your package manager (apt) with a new repository for this application.

The upside to that is that anytime you will look for updates, this app will also get updated.

It’s a bit more work up front, but it can pay off when you have dozens of app updating as part of normal system operations.

Imagine a world where windows updates would also update all your software, that’s what this is.