Not sure what you mean. I have a non-Nero ebike and I changed the speed limit to 99 kph but the bike physically only goes up about 28mph. If I do my part with shifting and pedaling I can get up to 32+ mph.
I believe that changing the speed limiter is for setting the speed at which the motor will stop providing power. In my case it should provide power no matter how fast I am going as I essentially removed the limiter. Though the motor and battery combination can only go so fast. Definitely not 99 kph. Setting the limit to 25 kph would mean that when I hit about 15.5 mph the motor would stop providing any additional power to help with my pedaling. It isn’t a physical speed limiter for the bike, i.e., speed/cruise control. At least I think that’s how it’s supposed to work. I could still go over 15.5 mph but I would have to pedal harder/faster. Also the Pedal Assist Setting may have something to with it. The lower the PAS the less power the motor will assist and the higher the PAS the more power it will provide to assist with pedaling. I’m new to this stuff so this may all be BS.