Don’t uninstall it before you’ve tested cosmic. Just select the Desktop you want to login with, make it default. When you’re comfortable with it, you can think about removing Plasma.

This is a bit more manual, so there isn’t a safe way.

You can get groups installed by enviroment with this:

dnf environment info kde-desktop-environment

You can then check the difference between your new installed cosmic environment and removing the differences or just remove the desktop group (in this case “kde-desktop”):

sudo dnf remove @kde-desktop

I’ve never done this, so be aware and check every step.

This maybe could try to delete packages even required by your new cosmic environment or other packages useful in general. Try to run the command and see what it lists to remove (do not confirm if not sure). This is a safer version which automatically says “no”, so you can just list changes:

sudo dnf remove --assumeno @kde-desktop

To remove only some packages in the group, list packages inside it:

dnf group info kde-desktop

And then manually write a dnf command to remove what you want:

sudo dnf remove kwin plasma-* kscreenlocker kdialog kdesplasma-addons [...]

Lemmy know how this process goes because I want to switch to COSMIC too in the near future.

Edit:

If you delete the old display manager (ie SDDM), remember to switch to the new one. I’m not sure if the system does it automatically. To switch do:

sudo systemctl enable cosmic-greeter.service

Cosmic greeter is the cosmic desktop display manager, if not installed install and enable it:

sudo dnf install cosmic-greater