Saying what is happening to your return at the IRS would be speculation. All you can do now is, wait. At least you know that the IRS has your filing. It does not matter who sent your form to them. That is the sole destination for federal tax returns. No one has discovered a way to make any tax agency speed up working on or sending out refunds. No one ever will because they are an overwhelmed, over worked, under funded and under staffed government bureaucracy. Eventually you will get the pay off of your no interest loan to the government. 21 days is just an educated/informed guess which should not be relied . Have you thought of paying just enough by estimates or withholding to avoid a penalty and let the government wait for your check?
Check
https://www.irs.gov/wheres-my-refund