You can apply for ESTA even if your accommodation reservation has not been completed yet.
However, if the application form requires you to enter a U.S. address or contact information, you should provide accurate information based on your currently planned accommodation or the first place you plan to visit.
If your accommodation has not been confirmed yet, it is better to prepare your information based on your current travel plans rather than entering a random address.
Please check your travel information carefully before applying for ESTA.