My main requirement is that I am using Syncthing to sync my notes from my Android phone, which uses Quillpad. Quillpad is amazing and looks super nice, and functional too, but all the notes are in one big folder rather than being subdivided by notebook. So I require a markdown editor that can create "notebooks" but don't change the folder structure of the notes (I tested putting notes in subfolders, and quillpad thought the notes were deleted. Silly Quillpad!)

So the notebooks/similar organisation of notes needs to be specific to the app and should not change the folder structure. I would prefer if the app is open-source too, and something that fits with my desktop (KDE Plasma) would be cool too :D

~~This rules out Obsidian (which puts notes in a folder structure. Obsidian is great, but won't sync well with Quillpad)~~, Joplin won't work either. Ghostwriter is pretty much a markdown notepad (quite good, but can't see all my notes in one place)

I am using EndeavourOS with KDE Plasma

edit: To clarify, I want a markdown editor that is able to separate notes into different groups without using folders as Quillpad doesn't like folders. I also need to have a way to view all the notes at once in each group

Using a code editor VSCodium wouldn't really work as there isn't really a way to organise notes, aside from putting them in folders (which I don't want), and I am not yet ready to jump into the Vim rabbit hole of plugins and configuration

edit 2: Markdown editor to note organiser to satisfy the pedant

edit 3: Looks like Obsidian has tags, so I could use those to organise notes without folders. I will try that and see if it works!

edit 4: Obsidian does have tags, but it seems like you sort by tags by typing tag:#NAME, and you can't use spaces for tags. So not Obsidian then unfortunately. Are there any other options that have a larger focus on tags or similar?