Removing duplicate rows based on a value in one of the two columns

Do you want a formula to give you the results in another place on the same/different sheet, or VBA to physically remove the rows?

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I am going to work with the data in post #1.
This proposal employs a helper column which may moved and/or hidden for aesthetic purposes.
The helper column is populated using: =IF(AND(B2="Unknown",COUNTIFS(A$2:A$8,A2)>1),0,1)
The formula that populates the final result, as modeled on sheet2, is:

Formula:

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