I think we would start with a meaningful decision that may impact an individual's human rights or health and safety. We would probably start with that as the basic definition. It is an area where I think considerable debate went on in the EU to clearly define what those exact use cases are.
There are even low-risk systems that you would want to.... You wouldn't even regulate all high-risk systems the same way. The questions you would ask would be different, and the risk assessments you would do would be different.