Currently, when switching to SQL expression display in the Label Class properties dialog in Pro, the SQL is totally unformatted, not even line breaks. This makes it almost impossible to maintain large SQL statements, as you need to scroll horizontally and don't have overview of the entire expression.
This issue does not occur in e.g. the comparable Definition Query text box of a layer, where the SQL has linebreaks automatically inserted for display, see image below. This should also happen in the above dialog.