Gimp should adopt the design language of its competitors Photoshop and Affinity Photo. Affinity largely looks and acts like a copy of PS when you open it up. That’s a good thing.
Also the name Gimp is really really terrible.
Also the name Gimp is really really terrible.
They also made some mockups of what a redesign might look like, but as you might imagine it would also be quite a lot of work to implement it: https://github.com/glimpse-editor/glimpse-nx-design
One problem with those designs is that cramming the entire GIMP's menu into the hamburger menu on top right is likely to cause more problems than it solves.
This stuff sort of works in applications with a limited feature set, such as Akira UX. I don't think it can work well for GIMP.
It's possible to find a hybrid approach, but so far, I've only seen Siril doing that, and I'm not convinced.
The designs are unfinished, but to me the idea was to move most of the functionality from the menubar into more tool options, or into smaller context-specific popup menus. I think if someone was to do a more extensive design review then that would be possible. But it would be a lot of work and changes to put on the users. And likely users would still want the menubar on MacOS where it's required. A good example of a really complex app I've seen that does it right is Blender. Siril is interesting for a GTK app, there is also GNOME Builder.
It's possible to move some of the nested menus into the main window. But as soon as you go anywere near filters, all hell breaks loose :)