There are a lot of different motors various mobility stuff uses. Which specific one do you have?
I can say that the "300w" 24v brushed motors I used on the original CrazyBike2 can handle up to at least around 48v ok, but they'll overheat quickly if you keep putting a lot of current thru them--I'd guess they might be able to shed the heat of about 300-400w of motor power (assuming you are using them at at least their rated RPM), without additional cooling.
The "600w" motors were larger and could probably shed the heat of 600-750w of motor power, I'd guess.
They can survive momentary bursts at much higher currents; IIRC I've put something like 2.5Kw (according to the wattmeter) thru one before the 4QD controller blew it's FETs, when I had a chain jam (which bent the rear axle and destroyed the rear wheel, and some chainrings along the way). But that was at most a few seconds.
I've also burned the commutator on one at much lower power.... :/
FWIW, 100A and 35v is 3500w, which is going to smoke that motor from overheating if you repeatedly hit that frequently.
But realistically, with as little load as the knee scooter has on it (unless you weigh half a ton or something
), that will be some massive torque (it might even damage the transaxle if it's slammed on repeatedly, so you might want to ramp up the throttle), and I am not sure you can actually use that much power on that little knee scooter.
Given the wheelbase, FWD is your only safe option at any significant torque, unless you want to break something else when it wheelies and flips you over on your back.