...I've only ever seen Fritz-Kola as a Berlin phenomenon tbh. There are some other regional brands though (e.g. in the Eastern German parts you're likely to see Vita Cola next to Coca Cola - completely different taste though).
[1]: https://www.handelsblatt.com/unternehmen/handel-konsumgueter...
One of the Colas that tastes good enough to replace Coke in my experience.
A bar owner I know here says selling these more-premium sodas is a good way to make a bit of extra money on people who aren't buying alcohol — you can charge more for Fritz-Kola than for Coca-Cola.
A different bar owner I know chose Jolly Cola, avoiding an American product but keeping a low price.