I want to connect my Windows 10 laptop to my television, the cable is on and the adapter, even if I press windows + p and select duplicate screen, there's still no source on the television
With MS Windows I think you still need some power… VGA can't bring that to HDMI by itself. I think it works at Apple.
The adapter costs more.
What does that mean roughly for me?
I think you have an adapter that only works for Apple, you need a Windows 10 compatible VGA to HDMI adapter
I'm assuming that the external (HDMI -?) Input must be selected by remote control on your television, as with my Sony.
How do I do that?
Whether and via which button the inputs are selected on your television can be found in the operating instructions for the device