Can anyone tell me how to take a photo ( selfie ) with the background in focus

It's known as depth of field. With a normal camera, the smaller the aperature, the more in focus close up and far away objects will appear, the larger the aperature, the less one or the other will be in focus. A bright sunny will close down the apreature more and give you the desired effect.

However, according to this article iPhones don't have a way to control an aperature so I'm not sure you can. If you move farther away from the phone, the focus will compensate and you may be able to get both in focus.

https://iphonephotographyschool.com/depth-of-field/

It would be better if you can please re-post with a screenshot, in order to understand the phenomenon better. Images / pictures speak louder than words. Do not provide any personal credentials, such as email id, apple id, IMEI number, Serial Number, Phone number, Order ID, if you are sharing a map ensure your location is not identifiable. Etc.