I found my solution. I upgraded to Windows 10 again but this time I kept my external monitor connected (the one with native resolution 1920x1080) and Windows 10 retained the correct resolution.

True, but Intel (the manufacturer) doesn't provide updates other than through Windows update, and Toshiba (it's a Toshiba laptop) offer only one update, nearly three years old, which seems to be for...

I'm not sure that my laptop even has a graphic card. I thought it was integrated, which is why there's no separate driver to update. But graphics is not something I really understand.

I also have this problem (No 1920x1080 resolution in Windows 10), but the only thing resembling a Video card I can see in my laptop specs is Intel(R) HD Graphics display adapter.

The Intel site...