Ubuntu 21.04 uses Wayland (vs X11) and packages a version of the geeqie image viewer that has a bug where this results in displaying white squares instead of images.

https://github.com/BestImageViewer/geeqie/issues/539

The workaround until Ubuntu updates their geeqie package is to go to Edit->Preferences in GeeQie and in the “Image” area enable the option “Use GPU acceleration via the Clutter library (requires restart)”. Once you close and re-start Geeqie, it works! (Assuming your graphics card supports GPU acceleration).