I recently created a Maplex label dictionary to abbreviate a full label (the entire field fill) to a single character. It worked great, then I uploaded it to ArcGIS Online and it wouldn't recognize it, it defaulted back.
I ended up writing an expression that solved that, but even the Esri support tech didn't know how to accomplish this, and said to create a new field, to which I answered "changing the schema for a label should be last resort", when it should just work.
The frustrating part is that the dictionary works so perfectly in Pro, but it's worthless if you can't leave that environment and it still work.
Here's 2 examples of what was needed to make it work with the expression on two slightly different generations of schema.
Here's the results.
I've only been learning Arcade for a year in my spare time, so while this looks stupid simple, it was not for me. Esri support not figuring it out after days of emailing back and forth, kinda lends credence to that as well.
I've never submitted an idea, but they said I should. Does this seem like it could help you?
Thanks, Alex