Assuming it's a relatively cheap e-bike with a motor on the rear wheel (a hub motor), that's likely the motor being starved out of phase amps that create torque, rather than the motor being weak. Especially if it's large and heavy Direct Drive motor with no internal gearing. These need a strong controller (power supply) to feed them current, as voltage doesn't matter for torque.
But generally it's not the motor itself that's weak, it's just got a weak power supply (and potentially weak battery BMS. Some controllers tie phase amp output to battery amp input by some 2 to 2.5x multiplication ratio.)
Going from a generic KT 22A controller to a 35A KT will give over +50% torque. Up till the motor hits magnetic saturation, torque scales linearly with the amps. The thinnest kind of direct drive (27mm magnets) can hit 80-90nm too. Most of those are 30mm nowadays and can push 100nm tho.
On the geared hub motor side, the G062 (most 750w bikes use clones of it) can push 90nm before there's a risk of stripping nylon gears. Smaller ones like the G310 may strip gears earlier. These generally need less amps to produce torque than direct drive, so they work better with poor electrical systems.
Worth mentioning that wheel size matters for torque on hub motors. Larger wheels need more torque to climb (thrust). And also motor wattage doesn't mean much for torque (phase amps from the controller and gearing affect that even on bikes sold with the same wattage rating).
I also find the throttle gatekeeping or wattage gatekeeping a bit silly. Going 25kmh by throttle or peddling has no difference in how dangerous a cyclist is on the road. They should cap top speed and acceleration on throttles, but banning them outright unless someone is doing a minimum cycling motion on the pedals is a wrong regulatory approach and limits accessibility.
Throttles above 6kmh (walk assist) are banned across the whole of Europe. Judging by how heavily the Netherlands pushed for the EU-wide throttle ban, and putting my tin foil hat on, I can assume this was done as regulatory capture to ban Chinese ebikes from local stores, as they come with throttles and aren't usually capped at 25kmh on pedal assist. Netherlands produced ebikes are all pedal assist only, mid-drive, and have very poor batteries and electrical stuff for the (over 2x) price they're sold for. And now they have less competition. EU also has a 45% tariff on "e-bike part" imports...
I would also like a regulatory framework to register and insure a faster e-bike (as imo they should not cap wattage and cripple the hill climbing torque, only speed/acceleration) for adults. Right now you can only register one that has a license in EU. If you build your own, it can never be legal, even if you have a motorcycle license and want to insure it. This class of e-bike is impossible to drive legally right now.
L1-b class registration can technically do this, but it needs the bike to be registered in Europe. No e-bike has this. No manufacturers sell class L1-b e-bikes registered in the EU. Only some electric motorcycles afaik.