It's not as useful for a man to reply to your revised question, but I have been to Cologne twice, and it is a wonderful city. It is unusual in that the majority of the major attractions are within walking distance of the HBF, which helps you with heavy pedestrian traffic, the essence of street-safety. Is your hotel walkable from the HBF?
I have also taken the modern subway in Cologne, but did not experience any problems.
It is true that there was a horrible incident in Cologne (2015) that involved anti-immigrant sentiment too, but I believe it also involved large, drunken crowds and poor police preparation. (Not that that this excuses right-wingers, only that you presumably would avoid that kind of setting anyway.)
I don't know if you will see the connection, but many people believe that New York City (where I visit twice a week) is today a desperate behavioral sink of street crime and transit violence. When normalized for a population of 8 million, New York is actually safer than many big cities, and safer than some semi-rural areas in the US. But there are obviously numerically more crimes reported in NYC than in my current suburban home town of 15,000. I don't want to get into politics too much, but when a politician refers to crime and the opponent's failings, he/she is not always making a factual statement!
https://community.ricksteves.com/travel-forum/germany/can-i-see-enough-of-cologne
I read this in the Seattle Times:
Last year saw the highest violent crime rate in 15 years, with an increase of 729 incidents per 100,000 residents in 2021 compared to 736 per 100,000 residents last year.
A similar number in NYC is 521 per 100,000, but in fairness, they are not from the same statistical study. I can't find a comparable statistic for Cologne. It is certainly not true that there is no crime in Germany, alas.
It's good news that you are familiar with a big city like Seattle. That means you probably have enough "street savvy" not to walk around the dark Cologne Altstadt alone at night, or to go down alleys you are not familiar with. On the other hand, there are a few Kolsch brewery pubs (just as an example of nightlife) that are almost within sight of the Dom (cathedral), and brightly lit and thronged at night.