Virtual machine (VM) software are basically emulators of computer systems. They run within an OS (host OS) and provide the functionality to install other systems (guest OSes) in an isolated environment. Lots of advantages for specific purposes, but have the downside that they share resources with the host OS, and certain apps don’t run as well as natively, among other things. If you want to give it a try, an easy way to start is to use GNOME Boxes, which comes preinstalled on the Workstation edition of Fedora.
But VM was a suggestion just to play around with another edition/spin of Fedora. However, easier than that is to run a live session of KDE Plasma (e.g. using either Fedora KDE Plasma Desktop, or Fedora Kinoite, in case the concept of atomic desktops is picking your interest). It’s the same situation as you’ve done to install Fedora Workstation, except you would log into the live session without starting the installation process. That way you would know whether Dolphin suits your needs.
Should you want to go for it, then either install just Dolphin, as suggested by you, or install KDE Plasma on your existing system (both with the downsides mentioned here and in the forums). Should you go installing KDE Plasma on your system, it is indeed a good option to create a new user, and proceed with the precautions discussed in this topic.
Either way, it is advisable to have your system backed up before you proceed.