You do not have to insert a SIM card from outside if your phone is eSIM supported. But this technology is not in all phones. It is really an amazing technology. It can be seen on very few smartphones. The Oppo Reno7 5G (China) is one of those phones that does not support eSIM.
Oppo Reno7 5G (China) is a smartphone full of various interesting features. However, this phone does not support an eSIM. You need to communicate using a physical SIM card. But there is an alternative to eSIM, that is wifi calling and this feature is supported on this phone.