If you’d like to request an enhancement, please do so on the GIMP gitlab: GNOME / GIMP · GitLab
Hi Zumamudin, welcome to the forum. Follow Mica’s advice about where to post feature request. However, why do you want a bigger icon? It seems that GIMP is as big as every other icon in your taskbar and mine. You will need to explain this when putting in a feature request.
I think it looks small due to its complexity compared to the other icons. The pointed parts of Wilber take up icon real estate (the brush, nose and ears). It bothers me but not enough to do anything about it. Some custom GIMP packages come with a more cartoonish rendition proportion-wise.
PS - I found this on the web - ha ha.