Could you please confirm that you are using a wired connection using a network cable which is directly plugged into your router. I also need the output of Start > Run > cmd > ipconfig /all

It's plugged into a range externer which is wireless connected to the router but I do have a wired connection to the range externer..
I attached the cmd and also after a disconnection from a game just lately so you can see how the game stops out of the blue

Try connecting your router directly with a long network cable and check whether the issue persists. If you don't have those random disconnects, then your problem is the Wireless Access Point.

I cannot connect my router to the computer, since it's too far away, it's in a different room...

Also, I already contacted my ISP and they told me all network tests are good, and the pc is plugged so I don't understand what's the problem if so far during the last few years it was all good with Voobly.

Yeah, but if there is a problem with your Wireless Access Point / Wireless Repeater, it literally explains all issues. Can't you buy a long network cable (30m) just to see, whether the issue is caused by your Wireless Access Point / Wireless Repeater.

They already restarted my repeater or range extender whatever you wanna call it, and I pruchased a new cable and none of those helped, and unfortunately it's quite impossible to set a cable between the pc and the router

Are you still there Chris?

Yes, I am.

So what's the solution of this issue? What do you think?

There is a problem (hardware or software) with one of your network devices, either the router itself or the repeater. Consider upgrading the firmware if possible — or replace it.