I would suggest gimp. It is the best free image editor, at least in my opinion.
To install gimp on debian
sudo apt-get install gimp
To install gimp on arch linux
sudo pacman -S gimp
You can also try installing it by flatpack.
flatpak install https://flathub.org/repo/appstream/org.gimp.GIMP.flatpakref
If you want gimp on windows, there are links on GIMP - Downloads.