Unable make DFF's Optional from create Purchase Order page and not able to see DFFs of edit page

Summary:

Unable make DFF's Optional from create Purchase Order page
As per Business requirement we want Supplier and Supplier Site field are optional when creating Purchase Order

and not able to see DFFs of edit page for Additional information
When created new Purchase Order in Additional information as per business requirement we want hide some fields Like Tender Reference, COC Decision etc.

but this DFF's are not able to see in VBS

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