[DiapDealer]

I discovered what was going wrong on Arch (and probably Manjaro as well):

When resizing/thumbnailing the images in the epub using Pillow's Image class, the plugin is using the Image.ANTIALIAS constant as a parameter. And that is what is silently failing on Archlinux. That's why no images show up when selecting them.

From what I can tell, all Pillow resizing methods have been Antialiased since Pillow 2.7.0. At that same time, ANTIALIAS was renamed to LANCZOS. The ANTIALIAS constant was left in for backward compatibility. So it's not necessary to use it.

Pillow has finally gotten around to removing the deprecated ANTIALIAS constant in Pillow v10, and that's the version of the python-pillow package in Arch's repositories. The version of Pillow included with the latest Windows and macOS versions of Sigil is Pillow 9.5.0.

So the bottom line is that the first version of Pillow included with Sigil was long, long, loooong after ANTIALIAS became unnecessary (Pillow 2.7.0). Remove it in the two places in the plugin and nothing will change (except that the plugin will work with newer versions of Pillow).