Today I use Adobe's Lightroom Classic for editing/enhancing photos. When I started editing photos as a Windows user, I used both Fast Stone Image Viewer and Google's Picasa for editing my photos. Fast Stone doesn't exist for Mac and Picasa was replaced with Google Photos.
Today, on the photographer sharing forum www.uglyhedgehog.com, a member recommended a free photo-editing application that others may find useful as their primary editing software -or- as a supplemental program for resizing, creating collages, etc. - PhotoPad. Take a look and see if it meets your needs.
Links: PhotoPad for Mac and PhotoPad for Windows
How to Use: PhotoPad Tutorial