Maybe things have changed and it isn’t that bad anymore. Doing a search for something along the lines of “installing multiple desktop environments” and you will see there are plenty of people suggesting to not do this. Probably just as many saying it’s usually fine. Note that the OP asked for a beginner friendly distro. That implies they might not be experienced enough to understand how some things work.

Saying “literally no problem about trying it out” is incorrect in my opinion and this applies to all contexts I can imagine, whether related to Linux or not. There is always a potential problem when trying something out. Nothing is idiot-proof or immune to wear and tear or perfectly free from bugs, software or literal. I personally am blessed with the uncanny ability to make the wrong choice in the majority of situations where I have a choice. That may even include the choice to make this reply.

Maybe for your use case, on the hardware you have, you haven’t had any issues, with the software you use. That doesn’t mean the issues don’t exist. I’ll mention again, do a search online. There are problems that can happen. They have happened recently. They have happened a lot. Not everyone has them.

I hate to come back to this example, since OP never stated they had it, but since you have ADHD, you may be familiar with analysis paralysis and executive dysfunction after being overwhelmed by too many things. Maybe forgetting which text editor worked best and seeing a dozen in the application launcher and start searching for the right one but by the time it is found the short term memory loss kicked in again and the original reason why it was needed has been forgotten. There could be frustration when starting to hyperfocus but an app is not working the way it did and so instead the night is spent grinding through preference menus already configured previously and eventually seeing that an update for one of the DE’s rewrote a config file or is using a differsion of python or it could be more than one of these things happening and one program also has a bug that spams the journal so troubleshooting becomes much more difficult… I’m digressing and projecting too much.

Have you ever uninstalled a DE after having more than one installed? Sure, it is possible. It’s easier and less time consuming to reinstall the whole OS in my experience. I’m not a professional, far from it. I know it didn’t go well. I can’t remember the specifics, I think I added a KDE package while using xfce and accidentally hit continue instead of cancel. It brought in all of KDE, which I didn’t want so I tried to remove it and everything broke because it removed shared xfce dependencies. It might be better now. I’d prefer not to try until I’m confident I know what I’m doing and what to do when things fail afterwards.

My point originally was, and still is, that it is often not recommended to do, especially for a beginner. I mean no malice towards you and hope this doesn’t seem aggressive or angry.