Question : while IR is super fast (once all the geometry is loaded), and rotation the viewport is very responsive, when you want to change the camera (while IR is running), the update of the IR is super slow.... Normal?
I cannot confirm anything of this. FPP v7.x + Corona v7.x is one of the best combos ever released. Even changing camera settings with activated autokey works without FPP rebuilds now. And IR does not restart anymore just because you keyed/changed the camera EV value.
There is just only one thing missing to make it perfect: when panning or zooming the view, all works smoothly. But if any rotation is involved, FPP starts to rebuild the scatter items again. According to Itoo it's a Corona issue and as a consequence, my expectations are high to get that last issue fixed for Corona v7.
I made all tests with Max 2021 (and 2020/2016 partially), so it may be again some Max issue? If you have the option to test with a different Max version, please do (and report back), thanks!
Good Luck