I have noticed that in the column definitions for all the virtual columns, including ref row/lists the option to make them required is greyed out - EXCEPT somehow I was able to add a required if expression for this one - am I crazy? Was this once an option that is no more?
It did use to be an option that is no longer available. The reason being is that all VCs are recalculated every single sync. And they only hold generated data. You can’t input data from the user directly into them, so there is no point trying to mark them required.