I have my PC a little further away from the mouse. Mouse cable is just enough, I plugged it in at the front. Does it make a difference or behind?

PS: I noticed yesterday at 1 vs 1 at Fortnite that the cable is too short. Now I try the USB port on the front. But it doesn't matter which USB port, whether at the front or at the back, right? Or is a bluetooth mouse better for 1 vs 1 ?!

Nope, USB2 is USB2 and USB3 is USB3 - no matter if front or back…

There are also extension cables available…

USB connection doesn't matter… I bought an extension cable and at the same time a mouse cable holder / guide or whatever they are called… Extremely practical! Now the cable no longer slips behind the desk:-)

In theory, you have a slightly higher latency at the front than at the rear directly on the mainboard.

But you will never notice this.

The problem is. I don't have a real gaming PC. Simply a 2-fold table… So I don't have to put the PC where I should.

Unfortunately I have no space for that. Where my monitor is, there's almost no space below for such a thing

What do you mean

As I said: give extension cables a try.

I do it with one of my computers like this: Extension cable from the PC to a mini USB hub, on which the keyboard and mouse are attached.

Huh how now? That the PC is closer to the mouse and keyboard?!

In practice it does not matter whether in front or in the back.

In theory, you have a low input lag with the front ones. But this is too small for it to have an impact.

Even if you are the super pro, you have a 800 hz sampling rate and a 400fps monitor, you will most likely not notice anything.

No, just the opposite! This means that the lengths of keyboard and mouse cables are really sufficient!