No, you cannot buy a house in Germany with Bitcoin. Since April 1, 2023, section 16a of the German Money Laundering Act has banned exactly that: the purchase price for a domestic property may not be settled in cash, nor in crypto-assets, gold, platinum or gemstones, whatever the amount involved. Your Bitcoin holdings still work as a down payment for a mortgage, but only along a single route: you sell them, have the euro amount paid into an account in your own name, and prove to the bank and the notary, without gaps, where the money came from.