The behaviour differs per city. Cyclists on sidewalks isn't tolerated in my city. Eventually they'll start checking and handing out fines.

What's super common is ignoring traffic lights. I also do that regularly. That's mostly due to pretty terrible traffic lights. IMO it just smooths things out.

What they hardly enforce is ensuring that cyclists have proper lights on their bike. Often nothing, sometimes something as bright as the a power indicator led (meaning: not at all). I often have trouble seeing such cyclists while cycling myself! They often also wear dark clothing and have a bike which doesn't have any reflectors.

When I lived in Amsterdam, the police always had campaigns at the start of winter to enforce bike lights. For a few days, police at major intersections would first remind and then fine cyclists who didn't have lights or whose batteries had gone flat over the summer. Very visible and hard to avoid. By the end of that week, nearly everyone was properly illuminated for the winter.

There are more bikes than people in The Netherlands, it's part politics, part ego (when I was on exchange in the south of NL I was told cyclists had assumed right of way no matter what)