A small and (hopefully!) simple suggestion:
Currently, the right-click context menu for sidebar menu items looks like this:
with “Open in New Tab” in the second menu group.
While Right Click Context Menu on links in the body of a document look like this:
And most browsers’ right-click menus look like some version of this:
With “Open in New Tab” first up.
Personally, I constantly stumble over this, clicking or almost-clicking “Add Subpage” when I want to perform the (far more common) Open in New Tab action. But I suspect I’m not the only one; this is a pretty common UI standard for right-clicking on links.
I think rearranging the side-bar Menu options would lead to a smoother and more predictable UX.