ArcGIS Pro 3.0.3; mobile geodatabase.
When creating a join via Add Join:
For cases where the join table has duplicate rows, it would be helpful if we could choose whether the join will be one-to-first (1:1) or 1:M.

Result:

Can an option be added to Add Join to explicitly choose either one-to-first or 1:M?
Related: Join — Control what related record gets used