upload bar is always green

I am a new Arduino user and I try to upload a very simple sketch.

void setup ( )
{
pinMode (8, OUTPUT); //pin 8 is set as output pin
}
void loop( ) // The loop function runs again and again
{
digitalWrite (8,HIGH); // Turn ON the LED on pin 8
delay (1000); //Wait for 1sec
digitalWrite (8, LOW); //Turn OFF the LED on pin 8
}

But it doesn't work.
I have connection to the UNO board (COM4) as it is shown in the Tools>Ports Menu. I use Win10.
As error message I get this after some seconds:

Arduino: 1.8.13 (Windows Store 1.8.42.0) (Windows 10), Board: "Arduino Uno"

Sketch uses 882 bytes (2%) of program storage space. Maximum is 32256 bytes.

Global variables use 9 bytes (0%) of dynamic memory, leaving 2039 bytes for local variables. Maximum is 2048 bytes.

C:\Program Files\WindowsApps\ArduinoLLC.ArduinoIDE_1.8.42.0_x86__mdqgnx93n4wtt\hardware\tools\avr/bin/avrdude -CC:\Program Files\WindowsApps\ArduinoLLC.ArduinoIDE_1.8.42.0_x86__mdqgnx93n4wtt\hardware\tools\avr/etc/avrdude.conf -v -patmega328p -carduino -PCOM4 -b115200 -D -Uflash:w:C:\Users\lange\AppData\Local\Temp\arduino_build_273615/sketch_oct07a.ino.hex:i

avrdude: Version 6.3-20190619

Copyright (c) 2000-2005 Brian Dean, http://www.bdmicro.com/

Copyright (c) 2007-2014 Joerg Wunsch

System wide configuration file is "C:\Program Files\WindowsApps\ArduinoLLC.ArduinoIDE_1.8.42.0_x86__mdqgnx93n4wtt\hardware\tools\avr/etc/avrdude.conf"

Using Port : COM4

Using Programmer : arduino

Overriding Baud Rate : 115200

avrdude: stk500_recv(): programmer is not responding

avrdude: stk500_getsync() attempt 1 of 10: not in sync: resp=0xe3

avrdude: stk500_recv(): programmer is not responding

avrdude: stk500_getsync() attempt 2 of 10: not in sync: resp=0xe3

avrdude: stk500_recv(): programmer is not responding

avrdude: stk500_getsync() attempt 3 of 10: not in sync: resp=0xe3

avrdude: stk500_recv(): programmer is not responding

avrdude: stk500_getsync() attempt 4 of 10: not in sync: resp=0xe3

avrdude: stk500_recv(): programmer is not responding

avrdude: stk500_getsync() attempt 5 of 10: not in sync: resp=0xe3

avrdude: stk500_recv(): programmer is not responding

avrdude: stk500_getsync() attempt 6 of 10: not in sync: resp=0xe3

avrdude: stk500_recv(): programmer is not responding

avrdude: stk500_getsync() attempt 7 of 10: not in sync: resp=0xe3

avrdude: stk500_recv(): programmer is not responding

avrdude: stk500_getsync() attempt 8 of 10: not in sync: resp=0xe3

avrdude: stk500_recv(): programmer is not responding

avrdude: stk500_getsync() attempt 9 of 10: not in sync: resp=0xe3

avrdude: stk500_recv(): programmer is not responding

avrdude: stk500_getsync() attempt 10 of 10: not in sync: resp=0xe3

avrdude done. Thank you.

Problem uploading to board. See http://www.arduino.cc/en/Guide/Troubleshooting#upload for suggestions.

I don't know what it means or what should I do next.
Maybe someone can help.

Remove any connections to pins 0 and 1 on your Arduino board. These pins are used for communication with your computer, including uploads. Connecting anything to these pins can interfere with uploads.

Make sure you have the correct board selected from the Tools > Board menu.

Make sure you have selected the port of your Arduino board from the Tools > Port menu.

Sometimes the port will be labeled with the board name in the menu. Other times it will not. If you don’t know which port is your Arduino board, you can find it like this:

  • Unplug your Arduino board from the computer.
  • Tools > Port
  • Note the ports, if any, listed in the menu.
  • Close the Tools menu. The ports list is only updated when the Tools menu is re-opened, so this step is essential.
  • Plug your Arduino board into the computer.
  • Tools > Port - The new port listed in the menu is your Arduino board.

Pin 0 and 1 are not connected with anything.
I have the UNO board and it is selected in the Board menu.
The board is connected with COM4. In the menu I can read: "Port: COM4 (Arduino Uno)"

So from my point of view, the connection is there and my computer recognize the board correctly.

Does the "L" LED on the Uno blink several times quickly after you press and release the reset button while the board is connected to the computer with the USB cable?

No, the "L" LED is not blinking. Just permanent "on" from the moment I connect the USB cable.
Only the "RX" LED is blinking, if I press the upload button.

OK, this indicates there is either something wrong with the bootloader firmware on the Uno’s ATmega328P microcontroller that handles the upload, or else that the ATmega328P is not working.

So the next step is to try to burn a fresh copy of the bootloader to the ATmega328P. This will require some hardware called an ISP programmer. If you don’t own an ISP programmer, you can use a spare Arduino board as an “Arduino as ISP” programmer:

Thank you.
I will get a spare first and then I will try it.