If what is wanted is a separate Qt-based gui, Acetoneiso qualifies: it is written in Qt and can mount and unmount images; it installs fuseiso and two qt packages.
But in spite of its name gnome-disk-utility only comes by itself with no packages foreign to KDE. It includes the gnome-disk-image-mounter tool which does the actual job.
To install:
sudo apt install gnome-disk-utility
To run "Disks":
gnome-disks
To mount an image file:
gnome-disk-image-mounter
or execute the file /usr/share/applications/gnome-disk-image-mounter.desktop. This executable is not found by the launcher as long as it contains the line NoDisplay=true; change that to false to launch it as any other program.
(then select the iso)
To add it to context menu:
kate ~/.local/share/kservices5/ServiceMenus/mount_gnomedisks.desktop
(be sure you have the folder ~/.local/share/kservices5/ServiceMenus)
then paste these lines:
[Desktop Entry] Actions=mount Icon=dialog-information MimeType=application/x-cd-image;application/x-raw-disk-image;model/x.stl-binary ServiceTypes=KonqPopupMenu/Plugin Type=Service X-KDE-Priority=TopLevel [Desktop Action mount] Exec=gnome-disk-image-mounter %U Icon=drive-removable-media Name=Mount image
and save.
And there are also the Dolphin services; most of those do not work, as they are outdated, and the newest ones are not the best rated. Luckily, there are exceptions, like KDE-Services (https://store.kde.org/p/998464). It seem it cannot be installed from the Dolphin-Services button; instead, it can be downloaded as tar.bz2 archive, unpacked and, by opening a terminal in the resulting folder, it can be installed by running the command sudo make install. This is a collection of services, desktop files installed at system level in /usr/share/kservices5/ServiceMenus/ and scripts installed in usr/share/applications.
To have a simplified service menu based on this, see this answer.