The dangers and opportunities are different.

Darkness, for example. My impression is that in a wilderness under the sky, it's rarely really dark. In any big building during a power cut it can be pitch black. It's more important to have a torch in an urban environment. This especially applies if you travel by underground train, use lifts or elevators etc.

You need tools for working with metal and plastic rather than wood and soil. A multi-tool which has a variety of screwdrivers is more useful in a city than in a forest.

There are more people around. That is a mixed blessing. There may be looters but there may also be emergency services. There's a high chance that someone will help you, if you need it. There are a lot of resources (eg canned food), but also a lot of people after them, which could be a problem. The organisation of these people becomes a big issue - eg the shear numbers can impede travel.

Shelter is probably easy to find. You are much less likely to need to make a fire. Where I live, everything burnable is owned by someone.

People become accustomed to things like piped water and grid electricity, and can be ill-equipped to cope when they fail.