There are 8 options available as per 3GPP shown at the below snapshot, so you can split the gNB at different points in protocol stack.
Moving from option 1 towards option 8 means high requirement for capacity and low latency and vice versa.
There is no single, ideal functional split because different options will suit different applications. It is, unlikely that the industry could practically supported all eight options. To ensure scale and openness, various industry alliances are working to gain consensus on the best options to be adopted.
But the O-RAN Alliance supports mainly option 7.2 for networks with high-capacity and high-reliability requirements. This functional split enables a relatively simple RU whose size and power consumption supports network densification and enables sharing by multiple operators, facilitating the developing neutral host market.