XnView MP is recommended for photographers, graphic designers, and anyone who needs to organize, view, and edit a large collection of images. It's also well-suited for users who require bulk processing and conversion of image files.
Shotwell is recommended for casual photographers, Linux users, and those who need a simple tool for photo viewing and basic editing. It suits individuals looking for an open-source solution with a focus on ease of use.
XnView MP stands for Multi Platform = it is available for Windows, Linux and MacOS. It is a continuation of the older XnView Classic. In my opinion it is a great alternative to Windows photos app or any Linux image viewer that comes preinstalled. I even think it is an alternative to IrfanView. It is really fast and simple to use, supports more than 500 image formats, has built in folder browser, image converter, editor... AND MORE!
IrfanView - IrfanView ... one of the most popular viewers worldwide.
digiKam - Professional Photo Management with the Power of Open Source
FastStone Image Viewer - FastStone Image Viewer is a fast, stable, user-friendly image browser, converter and editor.
Photos on macOS - Photos keeps your images organized and accessible. Rediscover favorite shots with Memories. Access them on your devices with iCloud Photos.
JPEGView - JPEGView is a small and fast viewer/editor for JPEG, BMP, PNG, GIF and TIFF images.
Movavi Photo Manager - Focus on the memories, forget about managing photos