You would have to find an exchange that operates in Germany. I'm in the US so I can't speak to the specifics of your jurisdiction. If Strike operates there I can recommend them as they will accept your Bitcoin deposit via lightning. Most exchanges have not implemented lightning so it would be a more complicated process to make a deposit. Kraken is another option.

You would probably have to give them a bunch of identity information regardless and then deposit the Bitcoin and sell it through their interface, then have them send the Euros to your bank account. There would likely be fees for selling and withdrawing.

You could also bypass some of this by selling on a p2p exchange like bisq or robosats. You can avoid a lot of red tape this way, but it's not as straightforward. I haven't used them ever, but there are plenty of explainers if you search. You may be able to sell them for a higher amount this way as these are non-KYC options and people pay a premium for that.

Personally I have never sold my Bitcoin for fiat, I only sell my fiat for Bitcoin. If you have any more questions I'm happy to answer and use the asknostr hashtag.