Krita seems to be having an issue specific to Solus. When one attempts to open a new image (File > Open...), the file manager that opens will not display or list any .PNG or .JPG images. It will display folders and allow you to navigate around, but image files will not be listed, even with the File of Type option set as 'All supported formats'
However, if you are in the correct directory to where you know the files to be, manually typing in the name of the image file and pressing enter (or clicking Open) will open the file in Krita as normal.
Also, if you manipulate an image in Krita and then export/save it somewhere, Krita will display it in the file manager. It seems it is only capable of listing/displaying images it has directly saved.
Saving/exporting a file with the native Solus version of Krita will result in the Appimage version from the Krita website unable to see it, and visa versa.