A German housing cooperative could help me find a family flat sooner, but renting requires buying shares. Is joining halal if it uses interest-based loans but I take none? Are annual dividends (e.g. 4%) halal, and does it matter whether they are discretionary or required by its bylaws?

If I have understood your question correctly (pls correct me if I have misunderstood), the answer would be that it is not allowed to buy shares in a company known to borrow from banks with interest, even if its main business is permissible. As for the dividends, if they are a fixed percentage of your capital required by the bylaws, that is not allowed, because in reality it is a loan with interest, and if they are a share of the actual profit, that is the valid way.