I've got a stacked label with multiple fields that I've been building in Arcade. Is there a way to add a halo to just some of my text, via tags or another means? Right now the whole thing is haloed, but I only want the top line to have that effect.
Nothing in the tags, HTML doesn't work.
Your only options seems to be creating two label classes. But then they will be positioned independently from each other. You can force them into the format you want with a a bit of fiddling.
For points, it's easy: the haloed class on top, the other class on the bottom:
You could also post an Idea to include HALO and _HALO label tags in ArcGIS Pro.