Can the i7 10 generation with a 2070 Max q on low settings manage a constant 240 fps in fortnite on laptop?
On a laptop?
these are good for playing at a high-end level as good as a children's bike for the tour de france.
neither do they have enough volume for cooling, nor do they have enough power. Everything is designed to save energy and mobility.
for your needs you need a high-end pc in the middle 4-digit € range.
If you don't have an external monitor, the 240 FPS won't do you any good.
If you haven't bought one yet, I would recommend a 140 Hz monitor.
It is less expensive than 240hz and more realistic with a laptop.
On a laptop, 240 fps won't do you much good. Since I very much doubt that your laptop has a 144hz monitor but rather 60hz. If you buy an external monitor, it will bring you something.
But what do you want at 240 fps if your screen can't transmit as many.
In your place I would rather play higher settings, then the game looks nicer. As long as you get constant 60fps.