There are a few different ways:

• VM: doesn’t give you the “real” experience. Often feels sluggish.
• Installation via package manager: really clutters and messes up your system. There are many dependencies, and then you’ll have 5 different file managers for example.
• Ventoy: the second best option, or the best, if you just wanna take a look at each. If you really want to try the DE for a few days, it isn’t suited of course.
• Fedora Atomic (immutable variants like Silverblue): there’s a project called uBlue, that provides images for all DEs. You can install the vanilla Silverblue, and then rebase to each according image. Your custom installed programs and personal data stay intact, but everything else gets swapped out cleanly. Each rebase would take ~5 minutes and one reboot, but it feels like you reinstalled your OS and changed the flavor.

You can install them all on any distro I believe. I use Arch and installing Plasma is just a single command, same with Gnome and the others. After install you can pick which desktop to use after the graphical login screen loads.

There are some annoyances, like for example if you have both Gnome and Plasma installed, and you type Files to open a file app, you get the Gnome file app even in Plasma since it’s named Files. To use the Plasma file app, you have to type Dolphin instead.

Same with settings app, I often open the Gnome settings app instead of the Plasma settings app by mistake since it’s called Settings.

But these are not bugs per se, it’s just because I’m used to typing something…

VMs are a way, but Live USB sticks are better because you will see how it actually runs on your bare metal machine, and if there see any hardware quirks, without comitting to an install