Can I try different desktop environments on Fedora, and what distro works best on a Razer laptop?

Fedora is the distribution: it provides the kernel, system libraries, package manager, and a large collection of software. KDE Plasma is a desktop environment, which includes the graphical shell and related tools such as the settings applications and file manager.

You can install multiple desktop environments on the same Fedora system and choose one from the session menu on the login screen. Your personal files and most applications will remain available. The main caveat is that each desktop may install its own versions of common tools, themes, settings, and services, so the system can become a little cluttered or occasionally have configuration conflicts. Using separate user accounts for different environments can reduce that, although many people run several DEs under one account without serious problems.

Trying several environments on an unused computer is a good way to compare them. You can also test complete distributions from live USB drives before installing anything. Installing two or three desktop environments on Fedora is possible, but removing one cleanly later can be more complicated than simply testing it in a virtual machine or on a spare drive.

A distribution with easier access to proprietary drivers may be less frustrating for a gaming-oriented laptop. Ubuntu-based options such as Lubuntu or Linux Mint are often convenient starting points because common proprietary components are easier to install. Fedora can work too, but it generally expects you to add some third-party repositories or drivers yourself.

I would test the hardware first rather than switching blindly. Since you are using a separate drive, keep the working installation intact and experiment with live USB sessions or another drive until you find a setup that handles the laptop properly.

For the Razer laptop, the exact model and GPU matter a lot. Check whether it uses NVIDIA graphics, hybrid graphics, unusual Wi-Fi hardware, or special keyboard and power-management controls. NVIDIA drivers in particular can still require extra setup, even though support has improved considerably.

Before choosing another distribution, try a current live image and verify graphics switching, suspend, Wi-Fi, audio, external displays, and battery life. A more hardware-focused distribution may provide proprietary drivers more conveniently, but no distribution can guarantee perfect support for every Razer model. Searching for Linux support specific to the exact model can reveal useful drivers and workarounds.