If you can create it in arc map or Pro, why does it not transfer to AGOL. This makes absolutely no sense. Please help.
The labeling engine in online maps is different than pro - so not all settings transfer. I would suggest setting up the labels in the map viewer, so you can see the limitations.
Configure labels (Map Viewer)—ArcGIS Online Help | Documentation
This did not work either. I am attempting to have the interstate shield appear on the interstate in AGOL.
If you are working with highway shields - I would use Vector Tile Style Editor (arcgis.com)
Highway shields are vector symbols, not a font supported in AGOL. Alternatively, you can publish points with those symbols.
To do highway shields the labeling should be done within the symbol. When you author the symbol the structure might look like this with a marker symbol using a text symbol and symbol property connection to the field.
Sample web map
https://jsapi.maps.arcgis.com/apps/mapviewer/index.html?webmap=24e519d4508747a8a7789230eaaafe10
I agree, what's the point of getting it looking good in ArcGIS Pro and then having to redo which heavy limitations in AGOL 😞