Comment 1 for bug 1799081

It is interesting that this is not reproducible in Lubuntu. We've apparently got something Ubuntu doesn't, which is strange, because we're quite similar at the core. Maybe try installing lubuntu-core or the lxde (or maybe lxde-core) metapackage and see if you can't figure out what you're missing. My guess is that this comes down to a missing package.

BTW: I would consider pcmanfm-qt as a separate project from pcmanfm. Admittedly PCMan. is the creator, but he hasn't contributed to pcmanfm since 2012 (https://git.lxde.org/gitweb/?p=lxde/pcmanfm.git;a=search;s=Hong+Jen+Yee+(PCMan);st=author). Instead, the primary contributor is Andriy Grytsenko (https://git.lxde.org/gitweb/?p=lxde/pcmanfm.git;a=search;s=Andriy+Grytsenko;st=author), unlike pcmanfm-qt where PCMan is still #1 (https://github.com/lxqt/pcmanfm-qt/commits?author=pcman)