We need to apply a workaround of enclosing the entire value component used in the case statement within double-quotes if there are multiple single-quoted values used in the expression.
So in the example above, we would need to put double-quotes around:
usecase_col_val in ('ABC','PQR','XYZ')
The entire statement would then have to be written as:
@case(~Var1~='ValueA', "usecase_col_val in ('ABC','PQR','XYZ')",~Var1~='ValueB',usecase_col_val in ('DEF'))@
Note that you do not need to use double quotes around: usecase_col_val in ('DEF'). This is because only one single-quoted value is referenced here, and the workaround needs to be applied only when multiple single-quoted values are used.