"Switcheroo" by @adhami is a fantastic batch image conversion utility for #GNOME, and it is one of the few ones that actually uses #MozJPEG for encoding #JPEG images. I use it to optimize my photographic images for the web (until #JXL takes over the web someday) emails, or other lightweight image purposes.
Much faster than the Yoga image optimizer (which uses an excruciatingly slow JPEG encoder at the moment) or than encoding images only one at a time with Squoosh!