I feel like I use this enough that a specialized wrapper expression would be helpful. IFERROR() exists in GSheets, and does exactly what I’m wanting, but maybe IFBLANK() is more in line with Appsheet expression naming.
IFBLANK( [column] , [second-column] )
…is equivalent to:
IF( ISBLANK( [column] ) , [second-column] , [column] )
…just a lot shorter, especially when you need to use a longer expression in place of