[suggestion] GtkHeaderBar counterintuitive button placement
Using GNOME Builder somewhat often, I tend to find the HeaderBar a little counterintuitive due to the number of popovers (6) and to the button placement that isn't always clear. For example, some Open/New actions are in the hamburger menu, some in the "Open" menu. And some buttons don't look like they need to be always shown.
Here are some personal suggestions to improve looks and usability of the HeaderBar contents: