On Kobo if you resize then the notes turn into an icon much like the Kindle's Sticky Notes. They also are stuck on the device and don't sync off of it. It really is very limited. Active Canvas will be an interesting compromise, but is still a limited way to do it where you still can't reference exactly a word or place on the page. You just get a text box that is anchored to a place.
https://help.kobo.com/hc/en-us/artic...o-Stylus#Three