I guess the affordances of the device influence what notes/annotations are likely to come into existence. On the Kindle, where IIRC input is through a keyboard (apart from highlighting), textual notes would be more common. On printed books and on the reMarkable (I'm even more "trigger-happy" on a reMarkable than on paper, probably because of undo and perfect erasing), annotation tends to be more free-form and varied, with more marks, scribbles, arrows etc, and a bit less text. Some of these annotations could also be understood and associated with corresponding text in principle, but it's not trivial. (Some examples of annotations from printed books: https://entropymag.org/writers-their-margin-notes/ )
I don't think so. The entire point of remarkable is to interact with the text. That is also How I have seen people use them at Uni. It's more like 99% of notes are tightly coupled to the text.