[ISBoxer] [WoW Classic] [OBS] Low FPS with screen capture

im duo-boxing in WoW Classic using ISBoxer.
I want to record video & mb stream.

Im using laptop - got 2 graphic cards (integrated Intel and descrete 1050ti).
Normally my ingame FPS is always 60 FPS. When Im using some video recorder (OBS, Bandicam) to record just one (!) game Window, it lowers to some 40 FPS which is fine but I dont see my other screen on recorded videos, obviously.

So... I want to record my whole screen, and so I need to use Screen capture. With Bandicam it worked from start but FPS goes down to like 10 FPS.
Then I tried to Screen capture in OBS - and i got black screen.. Then I read that I need to change graphic card in my NVidia App Settings specifically to use Integrated graphic card so it will capture my screen in OBS.... Aaaaand it worked, I do now capture my screen using Screen capture in OBS.

BUT FPS its soooo low, like 10-15 FPS.

What can I do? Im not very skilled in this whole theme regarding graphic cards etc...

Can someone help me pls? Thanks!

Capturing the entire desktop tends to require more resources than capturing just a single game client, even when said game client takes up the entire screen. So, I'd be looking at what the hardware is doing to see if there's a bottleneck somewhere.