Oh my god. I again failed to explain properly.
So when I switch between the applications, they do switch properly - there are no two applications open on the screen - but the "fade"? the transition? happens by moving to the side (like you know in powerpoints??) Am I making any sense at all???
Anyway, it's really not a big deal. But I'm used to the application switches happening without any transition on Windows
What you describe sounds like switching desktops rather than switching applications (within one desktop).
Do you have both applications on the same desktop? Or perhaps one is on a 2nd desktop and thus you're really switching desktops?
When I have Safari and Mail open on one desktop, for example, one atop the other, Command-Tab switches which is in front with no animations.
Hit F3 to bring up Mission Control and see if you have stuff on the two desktops.
https://support.apple.com/en-us/HT204100
I believe animations of desktop switching can be turned off -