I have already asked myself this question and found the following answers:
I have not yet found a document defining the approval in any of my e-scooters. I have already purchased 2 models up to 20km/h and 2 models up to 25km/h. The models all (Segway Ninebot and Xiaomi Mi pro 2 - by the way, the manufacturer is also Ninebot) have different driving modes. These can be easily switched.
Allegedly there are statements that the models are only allowed on the road if the models are basically and fixed limited to 20km/h. It is certain that operation above 20km/h is prohibited. But... there are also a lot of models sold that could also be 25km/h fast. If you want to be on the safe side, buy one that is limited to 20km/h. That's cool and insignificant. It's cool and not much slower!

Does anyone check this approval? if no one checks, you can also buy 55 km/h and never mind....

In Switzerland, all eScooters are automatically considered approved if they include the required components of a bicycle: Cat's eyes, front, rear, side, permanent light rear and front. In addition, the following riding modes are mandatory: Walk max 6km/h, Normal max 20km/h.

Switzerland is relatively easy with the law. In the EU, there are stricter rules depending on the country, e.g. a wattage limit of 300 W, compulsory number plate (D), compulsory helmet and special rules.

The best thing is to look at the regulations directly at ASTRA. There you will find everything from speed and compulsory helmet use to the colour of the reflector:
https://www.astra.admin.ch/dam...

Personally, all the electric scooters I've tried, thanks to my friends, are written 25 km, but on the flat! On a hill you will never reach 25 km!
And you have to count your weight, because the heavier you are, the slower it will go...

I did the experiment with me who weighs 54 kg and a friend who is 95!

There is no declaration document with it. This model, if not allowed on the road, should not be so declared by Digitec. And if you want to return it, it costs the buyer more than 20% of the purchase price (10% because of product opening, return costs by post + x% flat rate because of use). Welcome to the service desert that is Switzerland.