for the story, I created a similar app in the past (see https://play.google.com/store/apps/details?id=tagidea.standupweb&hl=en&gl=US) mainly for my own personal use, but when I stumbled upon simplenote.com I stopped caring about my project because it had everything I wanted, for free
I downloaded the app on mac and I tried writing. The app seems to work fine and is simple enough to understand in 2s, congrats, I know it's already not a small challenge.
I can just tell what features are missing for me to try it out as a replacement of my simplenote, if this one were to disappear or be expensive (fyi they don't charge me, but I would probably pay for the service they offer...). By order of importance:
1- Mobile app (sync'd)
2- Import/Export notes
3- tags
4- dark mode
Also I would probably be a little put off by the loading time of the app. I have a mac with a M1, maybe it's not optimize for it?
One thing that I liked about my project was that I called "folders", "books", it just felt better to write in them...