I'm pretty sure this used to work in the past: # emerge --depclean 'dex-texlive/*' However, right now it just exits after ~1.5 s with no output. '--verbose' doesn't help.
I have sys-apps/portage-2.3.76 and your command works fine on my system. However please notice there's a typo in your command: it should be "dev-texlive" instead of "dex-texlive".
Indeed, it works when spelled correctly. We should make it show a warning message if a given atom matches nothing.