I think this would benefit the entire Joplin community and everyone could agree on it being more integrated into the app at the top right such as many other programs. Otherwise we get a lot of empty and useless white space.
Incidentally this has become the norm on macOS Big Sur (albeit without a combined menu bar, just tool bar). It is also increasingly the norm on Gnome (see Geary and Gnome Files).
I was doing some digging, and apparently the combo title/toolbar is required by the Gnome Human Interface Guidelines. I opened an issue on the Joplin source repository reporting this as a bug: