I think your issue isnt necessarily KDE or Cinnamon issue. Once you are past kernel issues (if any), booting into specific DE should be easy.
]]>I uninstalled kde by -
sudo pacman -Rns plasma kde-applications
Wich packages did you install in the installation?
When you've already installed KDE you've also sddm. So you need to disable (systemctl disable sddm.service) and uninstall sddm (pacman -Rc sddm). After that you can go on and uninstall all installed plasma packages, then install all cinnamon packages, and then install gdm and don't forget to enable it (systemctl enable gdm)! After that you have to reboot, and cinnamon/must must be working.
EDIT: See also:
https://wiki.archlinux.org/index.php/Cinnamon
https://wiki.archlinux.org/index.php/Xorg
sudo pacman -Rns plasma kde-applications
This command and installed cinnamon packages and updated xorg-pacakages.
When I enable the gdm service it was saying there is already display-manager service running. So I disabled it .
Now when I start gdm service a black screen occurs and it stops there.
Please help with the same.