There is currently no way to get labels with callouts or leaders lines in vector tiles published to ArcGIS Online. Providing this would allow for detailed labels with less conflicts. I have also gotten an Enhancement logged with support ENH-000143760.
Here is my attempt with ArcGIS Pro 3.5
In Pro:
BrettFrahm_0-1762449355771.png
In Vector Tiles:
BrettFrahm_1-1762449403023.png