com.github.PintaProject.Pinta
Pinta is a image editing, drawing and painting application with a simple yet powerful interface. Pinta has a wide range of drawing tools, including: freehand, rectangles, circles and lines. It also has over 35 effects to apply to your images, and also has the ability to create unlimited layers to help organize your creativity.
Latest reviews
So far this appears to be the best feature for feature drop in replacement for Paint.net (which I love). The new 1.7 update seems promising as a lot of people were complaining about bugs and issues before. I observed no issues in this version. I just hope the Mint repository gets updated soon as the Flatpak of this app is a whopping 2.4 GB! The one thing I noticed is the app doesn't warn you when saving in a certain format will result in the image being flattened (it still flattens it but doesn't warn you). Not a huge deal as most people should be aware that this will happen but would be a nice touch.