Here is where Mike was explaining the two different entry locations for the Source:
tatewise wrote: ↑15 Sep 2023 17:53 FH is working correctly.
Your two methods attach the Source to different points in the data structure.
Option 1 attaches the Source to a subfield of the Individual Record where it links to the Media Record, so is not attached to the Media Record itself. In this case, when you select the linked Media the Source is shown in the Sources For yellow pane.
Option 2 attaches the Source directly to the Media Record. In this case, you must open the Media Property Box to see the Source in the Sources For yellow pane.