Conditional Formatting highlight duplicate values IF cell doesn't start with "XX"

I am trying to highlight duplicate values in a column IF the cell contents do not start with the letters "CB" (As there are duplicates which I dont want to highlight)

Can anyone enlighten me to a formula which will allow this?

e.g.
XA123 - Highlight as duplicate
CB123 - Do not highlight as starts with "CB" even though a duplicate
XB125
XA123 - Hghlight as duplicate
CB123 - Do not highlight as starts with "CB" even though a duplicate

Thanks for your help.

Hello
As an example for the range A1:A18, apply the following Conditional Format formula:

Formula:

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Does this do as required?

DBY

Many thanks this does indeed achive what I wanted.

I modified it slightly to include an OR statement as it transpired there were another set of items as well as the 'CB' ones, so it became:

=AND(COUNTIF($B$1:$B$1000,$B1)>1,OR(COUNTIF($B1,"CB*")=0),(COUNTIF($B1,"AP*")=0),(COUNTIF($B1,"LT*")=0))