https://gitlab.com/stavros/notes/
It's a bit ad-hoc, but it works well.
Been using Joplin for a couple years. It's one of those few open-source apps that managed to find a golden ratio of functionality but still to the point, a coherent pleasant experience across desktop and mobile.
Missing a basic collab or note sharing functionality though. It's all open formats and that, sure one could hack around it, but more in the spirit of mutual access to encrypted notebooks for example.
The sync works flawlessly and this is one of the strongest features it has.
I set it up using WebDAV and never ever had to worry about it working.
As far as E2EE note apps with mobile and desktop apps that sync go when I last looked in 2020, you have Standard Notes, Joplin, Inkdrop, Amplenote, Day One and DevonThink. I tried out Inkdrop seriously, but it wasn't better enough for me to switch and was more expensive than standard notes.
A lot of these apps are $5/month, and I feel like that is too much compared to the $3/month far more sophisticated utility apps like 1password are sold for.
I use it with NextCloud sync to a Heztner NextCloud instance. Data is all mine, they can even be E2E-encrypted if I want.
Now a healthy plugin ecosystem is forming as well.
I've already sent some money once or twice and I am actively looking for places where I can contribute code as well.
Recommending others consider that as well.