How can I disable this insane screen switching mess on my iMac desktop computer?

I am SO frustrated right now with this iMac and as a user of Mac exclusively since they were new on the market as Macintosh I'm so upset at how much less user friendly they've become in recent years that I'm seriously going to take a look at other systems to see if something is made for use by people like me who aren't code writers or born with a computer.

Ok, that said, my new problem with this thing began tonight somehow and I can't stop it. When I open an app the entire screen changes and what I'm working on vanishes. God only knows why anyone would need for this to occur but even more puzzling is how the heck do I stop it and can it be destroyed somehow so it never happens again?

A Google search showed a couple of suggestions, neither of which worked. When I click control and the up arrow the open windows all shrink down to the center of the screen. That's all that happens.

When I click on the Apple Menu the only thing that comes up are what you see in the pic attached which does not include "System Preferences", so I tried clicking on System Settings and when I do, there it goes again, the entire screen vanishes in that insane screen flip nightmare and nothing appears from clicking Settings unless it vanishes with everything else.

So, I'd love to know:

- if and how this screen flip thing can be completely disabled permanently, and:

-I'd like to find out what has happened to system preferences, and:

-where is Mission Control hidden now?

It's hard to get any work done when I have to spend hours trying to get my computer to function normally, and this flip problem has me completely unable to work at all until I can get rid of that bug.

Thank you very, very much.

I'm running OS 13.4. on a 35 month old, $3,600, 27-inch iMac with a 3.6 GHz 8-Core Intel Core i9 processor.

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