Well, we don't take separation of church and state as seriously as we should. The state collects the taxes for the churches, it's around 9% of your income tax. This happens automatically if you're baptized, and you have to leave the church if you don't want to pay this, which also happens at a government office.

I thought this was just a way to reduce money laundry. If the church would just receive donations, it gets hard to track where the money is coming from/going to. There's a church in Brazil that flies helicopters out of the temple carrying cash [1]. If you're a drug dealer there's no money laundry scheme better than this.

1. https://www.youtube.com/watch?v=Ciw8ciqPY_c

It has historical reasons. Back when Napoleon conquered Europe, the HRE redistributed some land from the Church to the secular rulers and in return promised to fund them via taxes and compensate them for the land. The church tax has since become more of a membership fee (you can just leave the Church and stop paying it), but the state still collects it for the Churches.

All your questions mostly answered, my unknown internet friend.

https://en.wikipedia.org/wiki/Church_tax

As a Blue Card holder, upon registration in town hall, they ask about your religion and if you don’t want to pay church tax, you have to say you have no religions. Germans also can get out of the church “in an official sense” and stop paying that tax.

I still show up as a parishioner at my old church. I haven't been in over 6 years.