Are you confused about different ways the city name is written? It’s simple - but beware, one variant sounds a little bit insulting to natives.
Düsseldorf is the original and official German spelling of the city name. It’s derived from the small river Düssel which joins into the Rhine here and dorf which means town.
As people outside German speaking countries usually don’t have umlaut letters like ü on their keyboards the letter is often replaced so it reads Dusseldorf. Which is, strictly speaking, a slight insult as the word Dussel means clumsy fool or moron in German.
So, what do do? Easy: In German, if umlaut letters ä/ö/ü are not available, they are replaced by the letter followed by “e”. So the official spelling of Düsseldorf without Umlaut is Duesseldorf, which is pronounced exactly the same.
That might save you from calling out people coming from a town of fools.