Devuan already supports Jpeg-XL (.jxl) image files in the form of libjxl 0.7.0
which is brought in with gimp, but this is not enough to enable thumbnailing of
.jxl files or viewing with your pic-viewer, what's needed is updated packages to
version 0.11.1 currently for bookworm. This adds thumbnailing and viewing support
when I tested at least in Mate/Caja/EOM-pic-viewer and Openbox/PcmanFM/Gpicview.

-Seems to be very quick and working well.-

Edit: The current Imagemagick 6 doesn't have support for the format, it is added in the next version in excalibur,
but unfortunately the right-click re-size and rotate functions in Caja and the ones I use in Openbox won't work
on this format until then. Perhaps it will get back-ported at some point. But this at least gives you
thumbnails and viewing ability without having to open gimp every time.

In general you should be wary about any software outside a stable Devuan repo, and
of guys who recommend using stuff from them in forum posts. You have been warned. lol.

This is all experimental stuff, the format itself is still new. This will not give
browsers the ability to view online .jxl images, only the google/mozilla overlords
can do that. Personally I believe in giving folks functionality whenever possible.

Latest packages:
https://github.com/libjxl/libjxl/releases?page=1

Archive package I chose:
jxl-debs-amd64-debian-bookworm-v0.11.1.tar.gz

Extract archive, and install just these three:

libjxl_0.11.1_amd64.deb
libjxl-gdk-pixbuf_0.11.1_amd64.deb
libjxl-gimp-plugin_0.11.1_amd64.deb