The IRS is running behind due to COVID and a huge amount of early tax returns being filed this year.
See this IRS newsroom release: https://www.irs.gov/newsroom/irs-operations-during-covid-19-mission-critical-functions-continue
They are so delayed that they postponed the filing date from April 15 to May 17.
21 days is not a magic number - it is just an average.
TurboTax only gives the general IRS (most returns are processed within 21 days) date. The actual date is known only by the IRS. TurboTax also does not adjust the general date for anything on the tax return. TurboTax receives no feedback from the IRS after filing.
The IRS says most refunds will be issued within 21 days - some faster, some longer.
(Most means more than half so many take longer - MUCH longer)
Each tax return is evaluated on it's own merits. There is no first-in-first-out. Two similar tax return submitted at the same time can have totally different processing times based on IRS criteria for examining tax returns that the IRS does not divulge.
Some returns will be held for ID verification or other verification. The IRS will send a letter if they require more information to process your tax return.
https://www.irs.gov/individuals/refund-timing
Check your refund stratus here:
https://www.irs.gov/refunds
Check your state refund here:
https://ttlc.intuit.com/questions/1899433-how-do-i-track-my-state-refund