No, neither of these work. My first one works ok in a VC.
I don’t have the choice of choosing column [System] in the App formula of column System.
The formula doesn’t give an error if I manually type it in but doesn’t work.
What kinda error are you getting? Do you want to display those values in Table UX? If so, you need to construct a VC, you can’t do it with the column values itself.
You’re attempting to apply an App formula to a non-virtual column (the System column). An App formula for a non-virtual column is only applied when the row is edited in a form or by an action.
Note, too, that giving a non-virtual column an App formula prevents user input for the column.
If you want to display a different value than input (or selected) by the user, you probably want to use a virtual column.