pc has already had this with Xbox game bar and the perf impact isnt really noticable. if I recall correctly modern gpus have some dedicated chips for video rendering that are otherwise idle. I would assume there is some hit to vram that could hurt if you’re limited on it, but for most people it should be fine.
I assume they meant check the wattage of the car charger output. some powerbanks have displays now and can show you it’s input or output.
… All phones also have displays and should show you the same thing but don’t.