The way the 2 graphics cards in macOS is supposed to work is that when an app creates an OpenGL context the system is supposed to automatically use the discrete GPU instead of the Intel integrated GPU unless the app has specifically requested to allow the integrated one (which MoI does not do):
https://developer.apple.com/library/archive/qa/qa1734/_index.html

Maybe you'll need to set an option in the OS as described here:
https://nathansnelgrove.com/how-to-force-your-macbook-pro-to-use-its-discrete-graphics-card-when-its-plugged-in/

Also this utility may help:
https://gfx.io/
https://www.howtogeek.com/288346/how-to-tell-which-graphics-chip-your-macbook-is-using-and-switch-it/

And there might be another setting for it here:
https://osxdaily.com/2017/01/08/disable-gpu-switching-macbook-pro/

- Michael