Hi @Iantaylor2050 ,
If I were to "draw" what I think your trying to do in Excel, I think the expected output would be this:

If this assumption is correct, then in the Items property of the Gallery, enter:
AddColumns(
'Your Data,
"isFirst",
!IsBlank(
LookUp(
ForAll(
GroupBy(
'Your Data',
"Your Serial Number Field",
"_GroupedItems"
),
{
_firstID: First(ThisRecord._GroupedItems).ID,//SharePoint ID
_serialNumber: ThisRecord.'Your Serial Number Field'
}
),
_firstID = ID,//SharePoint ID
_firstID
)
)
)
In the Visible property of the Icon in the Gallery, enter:
Boolean(ThisItem.isFirst)
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Imran-Ami Khan