First of all, everything I find seems to be an editor. I don't want an editor. I want a reader. I want a window that shows me the rendered markdown file, not its source. Sure, I don't care if it also edits, but if I cannot set it up to display just the rendered markdown on startup then it's not what I'm looking for.
Second, the few actual readers out there are browser based. I don't want to open the browser to read a rendered markdown file. I want a standalone window that does just that.
Lastly, I want the rendered markdown file to follow my GTK/QT theme, or at least have settings to do it.
I would prefer it to not be Electron-based.
The closest thing I've got to it is the terminal program Glow, but because it's a terminal program, it has some obvious limitations in its capability of rendering a markdown file.