Thank you for sharing the feedback here.
As mentioned by Rohith above Default Rule Set (DRS) 2.1 for the regional Web Application Firewall (WAF) is GA. Just sharing the announcement link again.
The "preview" text in Azure Portal above is a typo and has been reported internally and will be fixed soon. This is a cosmetic issue with portal and does not affect the functionality of the product.
Thank you once again for reporting this. Please let me know if you have any questions.
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