NOW OPEN SOURCE!!! Feel free to contribute:
https://github.com/ausdev16/QuickImg
QuickImg is a fast, simple, image viewer. No bloat. No cloud. No libraries. No projects. No danger of permanently editing images by mistake. Support for most common image file formats including jpeg, png, gif, tiff and heif (heic*, avci & avif).
***HEIF support requires Microsoft HEIF Image Extensions***
***AVCI/AVIF will both work with just the above Extension***
***HEIC support additionally requires Microsoft HEVC Video Extensions***
Just the right balance of functionality including opening, deletion, fitting image to window, actual pixels view, custom zoom, rotate, light/dark theme and fullscreen view.