Yes, I'm using Arcade expressions in Expression Builder in ArcPro 2.1.0.
My expression named BookPage:
IIF(IsEmpty($feature.book) && (IsEmpty($feature.page)), '', concatenate([Text($feature.book),Text($feature.page)], '/'))
My expression named qcxfer:
IIF(IsEmpty($feature.qt_book) && (IsEmpty($feature.qt_page)), '', concatenate([Text($feature.qt_book),Text($feature.qt_page)], '/'))