In Onshape, you can create your own configurations inside an Assembly regardless of whether or not you have Part Studio configurations. They are altogether separate and one is not important to the other.

Assembly configurations work mechanically the same way as Part Studio configurations. The difference is that in an Assembly, you can only configure Mates (not to be confused with Mate connectors), Instances, and patterns.

When more than one person is working in the same document, each sees their own selected configuration, except when working in Follow Mode; at that point the follower sees the configuration selected by the leader.

To learn more about Assembly configurations, you can follow the self-paced course here: Assembly configurations (Onshape account required).

Below is an example of an Assembly with the configuration panel icon on the right side of the window, shown below to the right of the red arrow:

Screenshot of Assembly with Configurations icon to access the configurations list