But in Germany you need an actual address. If you are homeless, you almost legally don't exist. You are prohibited from opening a bank account, for example, or having a job, because you do not exist.
You’re wrong, you have a legal right to a bank account (Basiskonto) if you live in the EU, even if you don’t have a fixed address. The bank literally can’t deny you ( https://www.bafin.de/DE/Verbraucher/Bank/Produkte/Basiskonto... ). You need to give them an address to send mail to, but that can be any address where you can get access to the mail (friends, family, homeless shelter…). Do you have a source for the claim?