What things are being messed up? You should be able to just install as many DEs as you want without them interfering with each other - just select which you want on the login screen,

In general it is safe to install as many DEs as you want. There is some overlap between (user) configuration files though which might be annoying.

It should be fine to experiment, but you might need to restore some settings afterwards. For daily use I would just stick to one DE. Personally I don’t think there is really a reason to use multiple DEs as a single user. It would throw me off and mess with my workflow.

Also keep in mind that many DE also provide a set of default tools which add clutter. So you probably want to keep it low for this reason alone.

I have kind of messed some things up by installing KDE on my Fedora that already has Gnome. This was almost a year ago, now. I would not advise doing this. It is a bigger hassle than it was worth, and I’m just looking forward to a free moment when I can wipe and clean install.

My Endeavour OS has Plasma, GNOME, Xfce, bspwm and Hyprland on it. I haven’t really had any problem with them.

Shouldn’t do much if you only have 1 other desktop. For example I used Pop!_OS for years which comes with Gnome, but I MUCH prefer KDE Plasma so I had that installed the whole time and just never touched Gnome (it was still there, removing it would have broken stuff).

There’s no one “proper” way. Running multiple DEs shouldn’t break anything, but each DE comes with it’s own set of dependencies and other software, so it does add clutter. There will also be considerable overlap with config files, so if you change a setting in one DE, it could change settings when using another DE.

Having a separate user account per DE will prevent most of the configuration overlap, but it doesn’t solve the abundance of packages you’ll have installed from having multiple DEs. I don’t think there’s a great “clean” way to do it.

One thing I love about Linux though, is how relatively flexible the user home directory is. When moving to a new distro or PC, usually everything you need to copy over is within your home directory. For what you’re trying to do, I’d consider throwing /home on a separate partition. That way, you can try out multiple DEs and distros, without blowing away your home folder. And you’d be surprised at how small your root partition can be, the vast majority of your storage should likely be reserved for /home. The Steam Deck, for example, uses a root partition that is only 5 gb. On a typical Linux system, I’ve found 64 gb to be plenty for root.

When switching distros and/or DEs, consider cleaning out various config files in your home folder. Almost all of them will be hidden files that have a filename that begins with a period. I only keep specific config files for programs I want to retain data for, like Google Chrome (.config/google-chrome), Thunderbird (.thunderbird), and Steam (.local/share/Steam). If you use SSH keys you’ll want to keep your .ssh folder too. But deleting all other config files will give you a pretty clean start when changing DEs.

I mostly use Sway (which is Wayland based) but also have Gnome and LXDE installed. I use one of those with X11 when I need to screenshare, because I can’t make that work on wayland. No real issues besides them having each others apps in their launcher menus.

Your DM should be able to handle multiple DEs just install from command line and pick which DE you want from the DM.

It can mess with configs, themes and some other annoying stuff so I never did it again but there is no big risk or anything, it’s just a little tedious to fix small things afterwards!

I haven’t had much issue installing multiple.

The biggest problem I’ve had is if you then want to uninstall one. Usually have to start over.

Something like nixos might be able to handle that much better.

I think usually if you use 1 DE per user, it works out fine.