It is common practice for companies to not provide a physical copy of the offer letter to employees in Singapore. The HR is correct in stating that the content of the offer letter is usually standard in terms of benefits, sick leave, annual leave, termination procedures, and probation period as per the guidelines set by the Ministry of Manpower. While it may seem unusual to not provide a copy or allow you to take a photo, it is within their rights to handle the offer letter in this way. It is advisable to make your own written record of the key details mentioned in the offer letter for your reference.