The only real solution probably is to do, like in IPv4, NAT between a fixed local network address and the dynamically assigned prefix of the day.
No, it’s not. The proper solution is readdressing of the network. If you still need some internal communication, you have Link-Local addresses - your printers or home automation will use LL for communication. Or you could configure additional ULA prefix.
Dynamic IP address in the way it is done in Germany is quite unique I think.
However the problem is really big in Germany, due to prefix changing every night with some ISPs, it is not unique to Germany. I’ve encountered it with my an LTE connection in another country when I have configured the Mikrotik LTE card to prefer another channel. After disconnecting and reconnecting to LTE I got a different IPv6 prefix and in the result lost IPv6 Internet access in LAN.