if I buy iphoneXR in japan can I use it in Indonesia?

Most phones purchased in Japan are SIM-locked, and most Japanese carriers will not unlock the phone. So if you are going to do that check very carefully that the phone is unlocked; get it in writing. the phone will have one physical SIM and one eSIM. The only dual SIM card phones are sold in mainland China and Hong Kong. And you still must be careful about getting a SIM-unlocked phone, although it's easier.