You are correct.Device manager and GpuZ finds only my onboard gpu.
But my rx 570 is plugged in and im "taking" picture from its hdma port.
I think there is an issue with my gpu but is it possible for a "dead" gpu to "give" image?
I think that your AMD drivers got corrupted and all you need to do is just reinstall them from scratch. Seems that when the external GPU is no longer present your bios goes back to your onboard GPU. You say you got an image, what resolution is this image? I am thinking you are running Windows using a non-AMD driver.
Just reinstall and see what happens. If you reinstall and you get an instant crash then most likely your GPU is bad. Because GPUs sometimes can work with the non-AMD drivers in windows and get a display, however once you actually install the proper drivers, it usually instantely crashes indicating that the GPU is bad.
Did you do anything recently to the GPU? Switched risers? Thermal paste job? Did it overheat? Etc?