Hi @Jennifer ，
If you are using the Retention policy which is managed via the Microsoft Purview compliance portal > Solutions > Data lifecycle management > Exchange (legacy) , agree with Vasil that you can create a Retention Policy Tag (RPT) to Notes folder and then add it into the current retention policy:
If you are using the retention compliance rule, you can use the Set-RetentionComplianceRule cmdlet which is available in Office 365 Security & Compliance Center PowerShell with the parameter -ExcludedItemClasses. See links below for reference:
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