I totally agree with what Lea wrote.
I would say in general, the bigger a city, the more people are used to foreigners and are friendly to foreigners.
But also the bigger the city, the more expensive the apartments are.
Finding a place to live has become quite difficult for everyone in Germany due to the housing market situation.
In my experience the best way of getting a place to live is over private contacts and tipps.
I grew up in Bavaria, so I can tell you a little more.
Munich (München) is a very nice but also extremely expensive city. Maybe the most expensive in Germany. If you want to still go there, make contact with Bellevue di Monaco. Its a project where a group of pro-refugee-activists took a whole building in the city center to provide it for refugees for living but also as a meeting point with a cafe and counceling. Even if you will not get anything there you can sit and chat and meet a lot of people who maybe can help.
If you look in the outskirts of munich, places to where the S-Bahn reaches. You will still find quite open-minded communities, as they are still very much connected with the big city-spirit of munich. Most of these villages have a so called Asyl-Helfer-Kreis, where a lot of nice volunteers try to help refugees as much as they can.
Then there are the smaller citys like Nürnberg, Regenburg, Augsburg, Passau
I know that Nurnberg as an traditional workers city has also an kind of left-wing-tradition and by the way a very good theatre scene and is maybe not so expensive.
Regensburg is a quite beautiful mediavel small town with a nice atmosphere because of carfree citycenter and a lot of students. A University is always a good sign for more open-minded people. But its depends very much also on what people study there. Regensburg has a lot of socialwork, pedagogues, and fine arts that means open minded people.
While Passau (also extremly beautiful with mediavel houses and three rivers) has a University for law and economics and people say, it is super conservative and tends to be more right-wing. But nothing is that simple. Because of that conservatism there is also an huge scene for political comedy and a very famous price can be won here for artist who go on stage against politics.
Then there is Augsburg, with a similar house project called the Grandhotel Cosmopolis. If you visit the city for a try, go there, drink a coffee and make friends.
If it comes to even smaller towns, it becomes harder to tell. There are towns I allways felt o.k., but I dont know how they treat a person from Africa. Just google images and see, if you like it. If you have a few names, you can contact me again and ask if I know anything about that town.
Also you might be more lucky to meet an African community (If you like that?) if you live in an bigger city.
You see, its not so easy to answer.
But keep looking and keep asking and especially ask people, friends, not just offices. That´s always the best.
Good luck and don´t hesitate to ask, if you want to know more.
Lots of love