We actually have a design site where we ask for user feedback and UX/UI improvement suggestions: https://gitlab.gnome.org/Teams/GIMP/Design/gimp-ux/-/work_it...
I share this link a lot in the hopes that more people take us up on it, and provide specifics on where problem areas are for their workflow. So many people use GIMP in so many different ways, even something that seems "obviously bad" to one group might not be encountered by others.