How do I change my DE from Gnome to KDE Plasma on Zorin 16.2?
If you search this forum for "Change DE" (or similar search term), you will find many threads and advice on the matter, including this one: [HOW TO] Install KDE (plasma), GNOME, XFCE, Cinnamon, MATE, Budgie, LXQt, LXDE and UKUI Dekstop Environments
You can install KDE by opening a terminal and entering:
sudo apt install kde-full
After installing, reboot and when you click on your user name at the login screen a cog should appear bottom right. Click on that and change from Zorin (default) to KDE (Plasma), then enter your password. After you have chosen KDE you won't have to select again at the next boot. Don't use KMail as anakondi is flaky. You will get an annoying popup KDE Wallet keyring. This can be disabled in privacy settings inside of System Settings.
Will this permanently replace Gnome with KDE as DE intead?
The OS will still be Zorin 16.2 right?
I just tried this and unlike before, I can't even tap click at all.
How do I change it back the way it was before?
Gnome is still present - you just go to login screen, at the login prompt select your username, the cog appears - click on Zorin Default.
To remove Plasma (KDE) open a terminal and enter:
sudo apt remove kde-full
Can I access the terminal before logging into my account?
Yes, press any combination of Alt+ F2 up to Alt+ F6 to get to a terminal.
In terms of touchpad issues, this fault help guide might help:
I can't access the terminal what button do I press?
Alt + F2/F6 not working.
My login screen is not same as it was before, how do I change it back?
Sorry, my bad - long day - up at 6.15 a.m. gritting the road!
Ctrl+ Alt+ F2 up to F6
Ctrl+ Alt + F7 will bring up the graphical environment
Can you take a picture of your login screen as it now is and post here?
Ok, it now says: tty4 login...
OK, so you are effectively at a terminal login - enter your username. It will then ask for your account password - note it might not show any dots or asterisks so be careful how you type. Once you have logged in, you should get to your computer name followed by $: indicating you are logged in to the system, albeit with no graphical interface. You can now run sudo commands as required but you may be asked for your password again to elevate you to root. If after login you see #: you are already root.
Once logged in to the system and you want to try and start the graphical interface, enter:
startx
and press return!
It now says only console users allowed...
How do I get rid of the new login menu that came after I had installed what you posted?
I don't like it and want to change it back.
Did you try using the sudo command?
I suspect you might have installed SDDM over gdm. Did you get a prompt about this?
Follow the guide on switching from lightdm to gdm - in your case it will be SDDM to GDM:
Yes I did install SDDM, do I redo everything again but this time install GDM instead?
Yes, I would remove kde with:
sudo apt remove kde-full
then reboot. If sddm is still there, try reinstalling kde as outlined in previous postand choose gdm. Otherwise might mean following the guide I posted earlier.