After updating the firmware now on my Fritzbox, and restarting, I got back to 14Mbit down and 876kbit up.

At the moment it is like this at my house. The main fibre outside is not connected yet, so at the moment, they still will pass through my normal cable inside the house, and there, the 30Mbit is the absolute maximum. Once they have connected all the houses, and connected evrything, then they can switch to other speeds, which are 100Mbit, 200Mbit or 1Gbit here. Although the 1Gbit is 150€/month.