How to make Project Number field mandatory on PO Line based on Business Unit?

Summary:

We want to make the Project Number field mandatory at PO Line Level. I tried doing that using sandbox. However, if I make 'Project Number' field mandatory, all the other project fields also become mandatory. This is still fine for us. However, I want to make it conditional, i.e. if Procurement Business Unit is BU1, only then make the POET fields mandatory. There is no option for Expression Builder on the Project Details panel form when I try using sandbox.

Is there a possible solution for this or is it no feasible in Oracle as of now?

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