Thank you for your reply, Michael. My BIOS is at the latest version. Official Asus BIOS Update Application verified that. About my laptop's vendor, Asus, it doesn't even suggest a driver for my graphic card (I think that's normal because it's AMD's responsibility).
Anyway, I really don't have any idea about what's the problem. Maybe my BIOS has some problems. When I had Linux, when I turned on the laptop, several firmware errors were displayed to me, which did not resolve even with the BIOS update and reinstallation of Linux. I don't remember the errors so I'm not sure if the problem is related to those errors. I think they start by "[Firmware Bug]". Well, I put some screenshots bellow that may help.

As you can see, AMD Radeon Software can't detect R8 GPU.

