The most recent incarnation (v3) fits your two criteria well and its plugin system is very versatile. Sadly cross platform supports only came with version 3 and that means saying goodbye to the small Windows native downloads, but it's not an Electron monstrosity.
Just a long time fan and always feel a bit disappointed that it never comes up in these kind of discussions :)
http://www.writemonkey.com/wm3/
(And in a pinch, away from my own machine, StackEdit is great.)
Yes, it's NW.js instead of Electron, but that's still an almost 100MB framework (and the >50MB sounds directory doesn't help much either). It's also closed source, though the documentation is hosted at GitHub: https://github.com/writemonkey/wm3/wiki/Documentation .
The sounds are from the zen/focus software trend days, when you have minimal distractions from the interface and background noise loops built in.
Just strange stuff like that.
I ended up switching to Bear for notes.
I use iA Writer for writing longer form stuff like documentation and where I need to work with files directly. It's a great app.
To sync, I use a git repository (you can set a watchpoint on macos and linux to any directory to invoke a command on changes, so I just invoke git and commit).
https://github.com/dunhamsteve/notesutils
The key for me is a) plain text files I can manage myself i.e. no database or mandatory custom sync; b) markdown.
Apps will come and go. You might decide to switch platforms and maybe a new editor will come along sometime. This means you want a format that can be opened by anything (plain text) but with lightweight markup that the editor can parse to make it look nice, but you can also parse with your eyes and get a reasonable sense of the document structure (markdown).
Then it's all about search. There's no point making notes if you can't find them. This is where something more than Markdown - that allows you to link notes - is handy. It's what is appearing more and more in the likes of Roam, Obsidian, etc.
I ultimately chose iA Writer on macOS because it is lightweight and really nicely designed, plus has good native support for Markdown. I sync using OneDrive but you can use anything because they're all individual files. iA Writer is also native, and I find most Electron apps to be slow and/or buggy. There are exceptions e.g. VS Code, but I prefer native where possible.