vindibona1, I have a Mavic Mini with its own phone - an iphone 6+ that was removed from my cellular carrier (Verizon) when I upgraded to the iphone 11. My other kit is a Mavic Pro hooked to a much newer ipad. I screen record and fly on that kit without problems. But the iphone 6+ CPU gets maxed out very easily when trying to screen record while flying. This is especially true in hot weather. If you don't need the audio, the cpu load is less, but then what's the point? Your 6s may perform a little better, but keep an eye out for the warning that appears in the upper left of your Go Fly screen. Once your CPU is completely loaded, scary things can start to happen, including sluggish response on the screen. Nobody likes that...
Best of luck with this. Let us know which solution works best for you.
Cheers