I wanted to shift to kubuntu LTS but I dont know if kubuntu have different softwares or special softwares as there are some software have 'K' in their name and some have 'G' in their name?
What difference does desktop environment like kde and gnome makes rather than look?

The windowmanager , the filemanager , the default programs used for the system settings etc

Do they have different softwares

yes as I said :

Gnome3 uses mutter as Windowmanager, nautilus as filemanager, file-roller for archives etc .

KDE uses Kwin as windowmanager, dolphin as filemanager, ark as archive manager.

After the base installations you can always add e.g Dolphin to Gnome or Nautilus to KDE, if you like.

So you won't miss anything you want, but you may need to install it on top of your DE

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You can install both Gnome and KDE in Ubuntu if you like. Then you just choose between them from your login screen depending on your mood that day.

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Once again if I install both dte then there will be problem of running software of gnome in kde and vice versa.
Do they support each others softwares?

You don't run Gnome in KDE you can run GTK+ Software in a KDE enviroment or you can run QT/KDE Software in a Gnome enviroment.

But you need to choose *ONE* Desktop enviroment (DE, WM) which doesn't stop you from running a Qt/KDE based program like Dolphin even when you choose to use Gnome as your DE.

You need to make a difference between the enviroment and the software with it's supporting libraries.

They don't need to support the other software (or they mostly don't do) because you need to have the libraries installed to use the software which is made for it .
So you need GTK+2/3 for "Gnome based" software and Qt/Kde-libs for "KDE based" software, even if you would choose openbox or fluxbox as your desktop enviroment .

These are two different things.

No Problem.