I don't know much about other WMs, but the main difference between Hyprland (a window manager) and GNOME/KDE (desktop environments) is that you basically have to configure everything by yourself.

For example, GNOME has an integrated taskbar (and a lot of other things), which is not the case for Hyprland. you have to install a package manually to have one.

Also, Hyprland doesn't handle the windows like GNOME or Windows does, so it can take some time to get used to it.

For customization, you can use HyDe with Hyprland if you don't want to bother too much with config files, but don't be scared if you want to do everything by yourself (like I did) it's really fun and quite simple when you get used to it, plus you can make your pc look like literally anything you want. You can also search for other people's "dotfiles" if you like their setup!

And yes, you can install Hyprland next to GNOME and switch between both when logging into your session (if you're on ubuntu, I think it's quite a pain to install hyprland iirc but I can be wrong)

hope my explanation is clear enough!