To connect it to all snaps which use gtk-common-themes, simply run:
for i in $(snap connections | grep gtk-common-themes:gtk-3-themes | awk '{print $2}'); do sudo snap connect $i adapta-theme-colorpack:gtk-3-themes; done
for i in $(snap connections | grep gtk-common-themes:gtk-2-themes | awk '{print $2}'); do sudo snap connect $i adapta-theme-colorpack:gtk-2-themes; done
The adapta-gtk-snap snap is from 2018 and it is possible that these GIMP icons were different at that time. I don’t know what the differences between the different Papirus variations are, but the gtk-common-themes includes the Papirus-Adapta-Maia, Papirus-Adapta-Nokto-Maia, Papirus-Dark-Maia, Papirus-Light-Maia and Papirus-Maia icon themes. These should be more up-to-date and might solve the GIMP problem. I haven’t tested it though.
Tista agreed to allow me to publish the gtk-theme-snap on some specific conditions.
If you are going to push derivative stuff please do make sure that everything is 1) credited and 2) licensed correctly.
Adapta is under GPL-v2 for codebase and CC-by-SA4 for SVG/PNG icon assets (dual license), then you should add ‘your’ packaging and publishing license and your credit to your resources for packaging if you had… For a while, it’s really hard to make my time to maintain Snap package(s) by myself, so you do if you want. Yeah that would be a nice feature for Snap users anyway.