where else are you supposed to ride eScoooters and bicycles?

On the road.

I agree that some people will get scared of being on the road with cars, but that's where they belong if there are no bike lanes. The catch-22 is that you can't get enough traffic to justify bike lanes until you have bike lanes. It takes someone to make the gamble that "if you build it, they will come". And, even then, drivers are going to be extremely dangerous. In the Netherlands, drivers largely aren't, but in North America there's a combination of drivers not expecting bikes, so making honest mistakes that get bikers killed, and drivers being evil assholes who don't think bikes belong near them and will drive dangerously and kill people.

Netherlands has reached a state where bikers feel safe because everyone bikes and it's safe. That means drivers always expect bikes. That makes biking safer, so more people are willing to bike.

Still, fundamentally, until there are bike lanes, bikes and scooters need to stay off sidewalks. Scooters and people who aren't experienced cyclists probably shouldn't ride on major roads either. Drivers are just too dangerous, and the speed difference between the two is too big. But, on smaller roads where the top speeds are about 30 km/h, the bikes and scooters will be going similar speeds to the cars. That's not that fast for a vehicle, but it's way too fast for the sidewalk.