There are some really dark areas in the game. Is there any way to get a flashlight, nightvision or something like that? So far I only found out how to activate light at cars, but no light source as human...

Same I thought there would be. Perhaps nightvision for the eye implants. Hell, even Geralt had a wooden torch...
As to the question I don't think there is. I've completed it once and never found any way of lighting up dark areas.

Flashlights exist in Cyberpunk 2077 world because at a point in time you can go on an underwater mission where ... ta da... you get a flashlight built into your swimming suit!!!!

Perhaps they only work underwater in 2077?

Flashlights are only for the LGBTQ community

Many of the dark areas have flood lights standing around that you can turn on.

I am missing a flashlight/nightvision in some areas.

I wonder why my combat optics that cost a mint don't have nigghtvision, heat vision, electromagnetic vision, etc.

Don't bring Common Sense into military related questions.

Why would anyone in 2077 use common sense when no one cares to use it now?