Linux

Here are three variants of Linux Mint with different Desktop Environments: (click their example image to make it larger)

• Linux Mint (Cinnamon Edition) - the default, I'd use that until you have a reason not to
• Linux Mint (MATE Edition)
• Linux Mint (XFCE Edition)

All of those are Linux Mint, they use pretty much the same core tools under the hood, but the desktop environments change how you engage with them. Mostly the way things look, the way you organize programs on your screen, and the default apps (like which text editor it comes with by default). This can change your experience a lot, I think Cinnamon looks nice and is smooth, while MATE and XFCE are more lightweight and might be better for older computers or if you don't like something about Cinnamon.

Now, those are all somewhat similar, they have a program start menu in the bottom left, a taskbar on the bottom, the basics are familiar. There are some (not officially supported by Mint) which are more different, like GNOME (Ubuntu's desktop default) which has a different app launcher instead of a start menu and a different way of switching between programs. Then, as others mentioned, some people choose to not even install a pre-designed Desktop Environment and only install some of the more core components of a DE, like the Window Manager. People who really love the keyboard might use a tiling window manager, these tend to make you think "wow, this person's a hacker", where they'll rapidly switch between programs using keyboard controls, with the window manager automatically shifting and dividing new windows so that they tile together to fill the screen. Loosely speaking, the opposite of a tiling window manager is a floating window manager, where windows just float and you move them around with your mouse, just like Windows (well, apart from the tiling options in more recent Windows versions when you can drag a window into the corner and it tiles to fill the screen.) I think the "best of both worlds" midpoint is a dynamic WM? I'm not sure. hyprland is an example of that.

If a computer is a car, then Linux(the Kernal) is the chassis. Mint (the distro) is the motor, and Cinnamon (the desktop environment) is the fancy interior.

KDE plasma is a fancy interior that works with tons of different motors.

Cinnamon is designed for mint and works best with it.

DISCLAIMER: All of this is analogy and isn't technically correct in a pedantic sense, but it works well enough for me. I'm sorry if my analogy isn't exactly accurate.

Okay, so the Linux ecosystem is more modular than Windows. Windows is synonymous with its Graphical User Interface (GUI) for reasons I'll get into later.

With Linux, there are several GUIs available to choose from. These tend to fall into two main categories: Tiling Window Managers, and Desktop Environments.

Tiling Window Managers have minimal on-screen UI elements, usually they're meant to be used with keyboard combos with little usage of the mouse. A major feature is everything that is running is visible on the screen, when you open a new window, another window divides in half to give it room, "tiling" the screen. Some examples of TWMs include i3 and Awesome.

Desktop Environments are going to be more familiar to newcomers from Windows or MacOS. They're made more for mouse control, several have what you would recognize as a taskbar, start menu and system tray. Windows can be stacked on top of each other like papers on a desktop, exactly like MS Windows does. Some more closely resemble MacOS though none behave exactly the same way. Some examples of DEs include Gnome, KDE, MATE, and Cinnamon.

Cinnamon is a DE made by the Linux Mint development community, and the default/flagship DE for Linux Mint. It is designed to be familiar and easy to use for Windows users. KDE's Plasma DE is similar in many ways to Mint although it's based on different tech; KDE is based on qt, Cinnamon is a distant fork of Gnome and based on GTK. Some are designed to be more minimal so they take up less system resources, like xfce and LXDE, others are trying mostly to resemble MacOS, like ElementaryOS' Pantheon DE. Then there's Gnome, which I goddamn hate.

For a beginner, the choice of DE is going to present most of the differences you'll notice when trying out distros. It can be instructive to try, say, Kubuntu and Fedora KDE. Both ship with the KDE Plasma desktop, but the underlying OSes are different. Then try out, say, Fedora Workstation (with the Gnome desktop) and Fedora KDE. That exercise will give you a good understanding of distro vs DE.

Edit to add: It's kind of like launchers on Android. You can go in the Google Play store and install a different launcher on your phone, you can make a Samsung Galaxy look like a Google Pixel. Linux DEs work the same way, you can install KDE or Cinnamon the same way you'd install a normal app, you can have multiple and switch between them. It's not a great idea but you can.

The desktop environment is all the stuff like the taskbar, the settings menus, the application launcher, the login screen, that kind of thing. It’s the system level user interface.

You choose which one by which distro you download. Linux mint uses cinnamon, Ubuntu and fedora use gnome. There are “flavors” of Ubuntu and fedora that use KDE. That’s why I suggested ventoy: you can download a few different ones and boot into them without making a new thumb drive.

If you don’t feel like bothering with any of that, just use Linux mint. It’s good.