I used to use Joplin, I liked that it integrated with my Nextcloud, and the markdown format. However, the way that it handles the markdown files was too black-boxey to me, with the way it split them up in a weird scheme.
Now I use Ghostwriter with straight markdown files inside my Nextcloud folder. So I still get the syncing functionality, but a more flexible setup that doesn’t require a specific app to access all of my notes.
I’ve been using wayblue on my own desktop. They have sane defaults & very pleasant theme. They do a good job keeping their image up to date & enable auto-updating from the get-go.