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!
digiKam - Professional Photo Management with the Power of Open Source
IrfanView - IrfanView ... one of the most popular viewers worldwide.
Photos on macOS - Photos keeps your images organized and accessible. Rediscover favorite shots with Memories. Access them on your devices with iCloud Photos.
FastStone Image Viewer - FastStone Image Viewer is a fast, stable, user-friendly image browser, converter and editor.
Movavi Photo Manager - Focus on the memories, forget about managing photos
JPEGView - JPEGView is a small and fast viewer/editor for JPEG, BMP, PNG, GIF and TIFF images.