There are many reasons why a federal refund may take longer than 21 days. I'm sharing a TurboTax FAQ below that may help you understand why your refund isn't approved yet.
https://ttlc.intuit.com/replies/3302330
*** I am NOT a tax expert. I am a seasoned TurboTax user, and volunteer to provide assistance to TT users. Nothing I post is to be considered TAX ADVICE; I bear no legal liability for responses.***