Hello!
I installed manjaro Gnome without knowing that Gnome now is outdated and I want to know if it’s possible to switch my DE to KDE instead… If so, pls consider explaining me how cuz I’m still new to linux
Nope. If you mean by that, you don’t have Gnome 41, you also say that KDE is outdated because you don’t have KDE 5.23 in Stable branch 
If you want to use most fresh (and bugged) software you should switch to Testing or Unstable. Manjaro’s target isn’t only most recent packages but also stability.
As @Tomek mentioned, your Gnome update cycle depends on the branch you are using, Unstable runs already Gnome 41.
Changing a desktop environment (if it’s not a neighboring version) is best done by a re-installation, backup your data, first.
you can install additional kde desktop environment as:
sudo pacman -Syu plasma-desktop dolphin konsole
This is not a good idea @clubberlang as mixing packages from two quiet different desktop environments usually causes issues as these packages don’t play nice together. In addition, it is pretty difficult to remove one desktop environment if another is installed in addition. Only way to avoid these kind of troubles is a clean re-install.
The subject has been discussed many times here already, please use the search engine to find the corresponding threads.