@JayJohnsonWashoeCounty
I had the same issue. A thousands separator was displayed when numeric field values are used in labels, and pop-ups in ArcGIS Online or Enterprise. This was a problem when displaying acquisition year for aerial photographs.
To resolve this in pop-ups: I used the Round function, with the number of decimal places set to 0.
Example:
"Round(($feature.ACQUISITION_YEAR),0)"
For List elements in ArcGIS Dashboards: I used the Text function, with "0" for the digit format.
Example:
"return GroupBy(fs,[Text('EQUIP_NUM',0),'DATE','CAMP_NAME','ROAD_SEG','FUNCTIONAL_ROAD_CLASS'], "
I hope this helps.