As I said, the RPI 4 is as it should be. Should I reinstall the OS again? What do you think?
Yes, it is a good idea.
When there is a hard to debug problem, I start with easiest to harder solution as follows:
(1) First re-image the microSD card with
freshly downloaded OS image. If you are using RaspberryPi imager, it saves the downloaded image in its cache. If you again use it, it wont download a fresh copy. Instead it uses cached copy. If this cached copy got corrupted during original download, the reimaging will again have the same corruption.
To avoid this, before re-imaging, I delete the contents of Imager's cache folder
C:\Users\abcd\AppData\Local\Raspberry Pi\Imager\cache
(2) If re-imaging does not fix the issue, I use another microSD card and write fresh image on it.
(3) If that also fails then the problem is most likely in the hardware (Poor or Failing Power Supply Unit, Loose USB terminal, Bad USB extender cable, and if all this is OK, then the Pi itself)