Smaller UI
The UI does not have to always be visible. When i am taking notes i just want a FULLSCREEN (see that idea too) paper and maybe a widget on one of the edges for changing the color or the thickness of my pen. I don't need to have the save and delete and bookmark and tabs and title and everything on top of the paper. Just tools and colors. For more there should be a pop-up menu or something.
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Cassio Magalhaes commented
I've been waiting for them to implement this for years. A simple tap with 4 fingers, like on Procreate, could make the toolbar disappear/reappear while allowing user to switch between pencil/eraser with the Apple Pencil itself. Please gives us the option to remove the UI completely and immerse ourselves in the process of note taking.