I needed an ISO one day and noticed Dolphin has no mount option at all. Nautilus does this, so why not Dolphin?
The problem
There was no simple way from inside the file manager. Mounting from the terminal works, but typing it out for every file gets old fast.
The fix
A context-menu entry was added that takes the ISO file and mounts it automatically:
udisksctl loop-setup -f "$1"
udisksctl mount -b /dev/loop0
The whole project lives in the iso-mount-kde repo.
Note
If the mount doesn’t come back, check dmesg | tail first — the problem is usually the loop device, not the file itself.