When saving Arcade expressions from the field calculator, they save as .cal files. If you want to import this expression for use in symbology, you cannot, as the import dialog only allows you to view .lxp files. Are the .lxp files really any different from .lab? Aren't they both just text files with the expression inside and a proprietary extension? And if so, why not allow for any .lab or .lxp file (or .txt for that matter) to be selected for import in either circumstance? I understand there are some differences in syntax and capabilities of a given Arcade profile but it seems that in many cases, the differences are irrelevant. That's one of the many uses for the Validate button. I made a copy of my .lab, renamed it .lxp, and it worked just fine.
recent related info at least for lxp and its text/curly brace-ed-ness
Use IDE for writing Arcade expressions - Esri Community
Awesome, was wondering if VSCode would be serviceable.