GIMP is available for Linux, Windows and MacOS. According to the GIMP website -
“The Free & Open Source Image Editor
This is the official website of the GNU Image Manipulation Program (GIMP). GIMP is a cross-platform image editor available for GNU/Linux, OS X, Windows and more operating systems. It is free software, you can change its source code and distribute your changes.
Whether you are a graphic designer, photographer, illustrator, or scientist, GIMP provides you with sophisticated tools to get your job done. You can further enhance your productivity with GIMP thanks to many customization options and 3rd party plugins.”
A couple of experts on YouTube in GIMP are Logos by Nick and Davies Media Design. Check them out.
Krita