Is it permissible to obtain a fixed annual return for several years by leasing an apartment at a specific annual rate through a contract with the developer company that owns the apartment, knowing that the company is part of a group that includes branches dealing in the global stock market? And is it permissible to deal with this company?

If you purchase an apartment from a company and then lease it back to them, without this being stipulated in the sales contract, then there is no issue with the permissibility of the transaction. Similarly, appointing the company to lease it on your behalf for a known percentage is permissible. The company's involvement in some forbidden activities does not prevent dealing with them in permissible matters. However, if the lease or agency is stipulated in the sales contract, the majority of scholars consider the contract invalid.