Nano: All digital pins do not output anything
Your sketch works on a Nano (clone) that I have

I am using a high-brightness white LED with a 10kΩ resistor to bring the brightness down to a bearable level, so the current drawn is about (5v-2.2v)/10kΩ = 0.28mA. This is a low level of current and should be safe for poking around with.

I can see the embedded LED blink if I program the Pin 13, but no impact outside of it.

That suggests that the ATmega328P is essentially undamaged and that at least the IC leg connected to D13 is working as it should.

How can I actually find out if, by any chance, I successfully (!) damaged all my digital pins?

Without a multimeter or other tools,  I would take a LED and resistor that draw less than 5mA, test them between VCC and GND to make sure they work
Then I would use the resistor and LED to check the output of each of the D2 to D13 outputs using your existing sketch.
When the onboard LED blinks, I am able to attach a LED and series resistor to pin D13 and get it to blink.

I wasn't sure what you intended by setting in to 8 so I later changed your program as follows:
const char  in=A1;

and I got this output on the serial monitor after connecting a jump lead from D13 to A1
0
1010
0
1009
0
1009
0
1009
0
1009
0
1009
0
1009
0
1009
0
1008


If I pivot the LED away from pin D13, I can use a jump lead as a test probe

Main points:

pick a high resistor value that minimises current drawn but is still easily visible.
check the LED works! (is right way around etc)
use a jump lead as a probe.

There are more sophisticated test circuits you could build with a FET etc but this would normally be enough for me to decide if an Arduino's outputs are damaged.

Extract from ATmega328 datasheet - note the max current draw per pin is 40mA. Exceeding that is probably the easiest way to damage the IC but if the onboard LED labelled &quot;L&quot; (and connected to D13) works, it means that part of the IC is undamaged.