How to make Revenue line Item Amount as read only or not-updatable conditionally?

Summary:

When the revenue line is CloseWon, we do not want the Revenue Line amount to be changed.

A new data field, Opportunity Revenue - Fields - Amount (API SplitParentRevnAmt) instead of RevnAmt is holding the line revenue amount; this data field Updatable condition is not editable.

How to make this data field conditionally locked or Ready only or not-updatable?

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Version (include the version you are using, if applicable):

NextGen Redwood Sales

Code Snippet (add any code snippets that support your topic, if applicable):