When I tried the joplin app 9 months ago, the mobile app on iOS was just plain broken.

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.

For Joplin, review the sync settings. Sorry I forget which one it is but on iOS there was a bad default and once you change it the mobile app works like a dream.

No it was broken to the point where I couldn't even just write a note with a keyboard properly. Even if that was fixed the fact you have to change a bad default out of the box is indicative alone.

Sync settings in the iOS or on the desktop app?

iOS app!