Thats simply not true. Its just that Germany has rules against demanding the extinction of the state of Israel – you know – due to historical reasons and mainly against Nazis.
The claim ‘from the river to the sea’ calls for the extinction of Israel, because it calls for a Palestinian state between Jordan and Mediterranean, therefore Israel has be desolved. Therefore ‘from the river to the sea’ is a prohibited phrase in Germany and you are not allowed to chant it at demonstrations. If you do so, the demonstration might get cancelled.
Freedom of speech in Germany is just more restricted compared to the US. There are a lot of things you are not allowed to say – mainly things associated with Nazis.
The US – like Russia and China and a couple more countries – doesnt recognize to the ICC.