I also post this question in ESRI community here :
https://community.esri.com/t5/arcgis-online-questions/feature-layer-failed-to-support-arcade-label/m-p/1364551#M56532
arcade label format tag
https://pro.arcgis.com/en/pro-app/latest/help/mapping/text/text-formatting-tags.htm
Arcade label in arcpro works fine
When I publish as feature layer on arcgis online and arcgis portal, the label failed.
https://palmspringsca.maps.arcgis.com/home/item.html?id=93756247f383480b9fe5cb890390e7c3#visualize
solution
ESRI have not fix this issue, since 6 years ago, someone post it. Up to today, arcgis online still not support arcade label.
https://community.esri.com/t5/arcgis-online-questions/confused-about-arcade-labeling-compatibility/td-p/570695
Work around is to avoid use arcade tag
Final result, labe fixed
https://palmspringsca.maps.arcgis.com/home/item.html?id=93756247f383480b9fe5cb890390e7c3&view=table&sortOrder=desc&sortField=defaultFSOrder#visualize