How do I stop iCloud from moving my desktop files to the cloud without permission?

We are not Apple; folks who read these posts are just users like you. In any case, we can't know how you have your Mac set up unless you give us some details. I'm pretty sure the Mac doesn't "move all my files to the cloud and off my desktop without … permission," but you may not have known when you gave permission. I certainly don't read all those things that pop up asking me to read and agree to!

So, how have you set up your Mac? When I go to Settings>[name]>iCloud, it looks like this:

and I can see that I have gotten a bunch of stuff stored in iCloud. If I click on iCloud Drive

I see that I have turned on iCloud Drive, and I've agreed to synchronize my Desktop and Documents folders. I have chosen not to use "Optimize Storage" with iCloud Drive.

If in the "iCloud" section, I click on "See All," it looks like this:

with lots of stuff turned on, and some stuff turned off. So, what does yours look like? Is that what you want?

Perhaps you should see this:

Understanding iCloud Drive - Apple Community

Let us know what you have, and what you want-- we may be able to help if we have some details…