ArcGIS Pro 2.9.5; Oracle 18c 10.7.1 EGDB:
I'm using the Make Aggregation Query Layer tool to join from an FC to a table. Both items have an ObjectID field, as expected.
The Unique Identifier Field parameter seems to be mandatory. An ObjectID field is listed in the parameter picklist by default.

What item does the ObjectID field pertain to? The FC or the table? My best guess is the ObjectID field belongs to the FC (the Target Feature Class). But I am wondering if the tool could make it more obvious.
Related Esri Support cases:
03651040 Make Aggregation Query Layer - Target Feature Class "table not found" error
03651111 Make Aggregation Query Layer - ERROR 000840 Target Feature Class parameter
03651113 Make Aggregation Query Layer - Error 000358 No fields can be mapped to unique identifier