Somehow it must be related to DHCP. The Router write " Broadcasting Dhcp_discover", but why is that if I put the Fritzbox on the router?

It works: šŸ’Ŗ
After changing the Static ip.
New: M552 P192.168.1.121 S1
Old: M552 P192.168.178.121 S1

I think it comes from the Router.
šŸ¤˜