Welcome!
I also run Linux, but still do my photo processing on a Win system. A decent CPU can run Win applications in Linux nicely with wine. Here is how I have run Faststone Image Viewer on my Linux machine: Install wine (the exact process depends on your Linux variant), then download the latest version of FastStone Image Viewer from here:
FastStone Image Viewer, Screen Capture, Photo Resizer .... If you download the installer (.exe file), you can install it in wine (double-click the .exe installer) and you should be presented with a desktop icon to click on to run FastStone. Or, you can download the portable version of it, extract the .zip file into a directory, drill down to that directory with your GUI file manager and double-click on the FastStone .exe file. It's fairly seamless, and seems to perform well, even on my old machines.
This process actually works well with *many* Win programs on Linux, especially if you have a fairly well provisioned CPU (# cores and RAM).
-Joe-