Helsinki has cars and sidewalks everywhere, but it still isn't really walkable. A very typical distance from where people live to where any necessary services are is 10 to 15 km. That's a 2½ h to 4 h walk. per direction.
It's a bicyclable city, but even that just barely. And that requires a rather fast bicycling speed, which causes its own problems, especially since we had the SCAFT street design philosophy for a long time, promoting an idea that riding a bicycle is just a form of being a pedestrian.
So, you can definitely have a city that has sidewalks everywhere but is still not realistically walkable. The core of the city is, though, but living there is expensive, so in Helsinki only the richest have the privilege to live in a walkable city.
EDIT: Found a random Youtube video that showcases the walkability of Helsinki very well. It begins in a suburb and takes the shortest way to a hipster area near the centre of Helsinki. 24 km. Could be walked, but not many want to. The city is applauded for being very lush and green. But. The distances are a very slightly little bit excessive-ish?