jpegtran has a "-crop" flag which performs lossless cropping of jpeg images as long as the crop is to a multiple of what the manpage calls the "iMCU boundary", usually an 8x8 or 16x16 block of pixels.

See https://github.com/jepler/cropgui for more details and https://bugs.kde.org/show_bug.cgi?id=204135 for how this was inplemented in digikam.

What I most like gwenview's crop tool, which I have incorporated into my workflow, is that you can enter the crop limit values by hand. It would be nice if it had support for this kind of cropping.