I received form letter 4883C from IRS and was able to verify my identity on 5/1. It has been almost 3 weeks and still no refund. Has anyone experienced a similar situation?

Unfortunately TurboTax gets no information about the status of your refund.
In normal times, the IRS says that most filers get their refunds within 21 days from the time their tax return is accepted.
Many returns are taking longer now since the IRS did not process returns for a while and there is now a big backlog of unprocessed returns.
The IRS has started reopening offices and processing centers and are starting to process mailed returns and other paperwork again after not processing any for several weeks.
They are now taking phone calls with a limited staff but it's hard to get through.

If you efiled your return, have you confirmed that the return was submitted by TurboTax and accepted by the IRS?
https://shop.turbotax.intuit.com/efile/efile_status_lookup.jsp

If accepted, what does the IRS tracking web site say about the status of your refund?
https://www.irs.gov/refunds

Here is an IRS Q&A with information about refunds:
https://www.irs.gov/refunds/tax-season-refund-frequently-asked-questions

Once your return has been accepted by the IRS, the refund process is completely under the control of the IRS. The IRS says that most refunds would be issued within 21 days. But some returns need more processing and refunds will take longer, especially during these Covid-19 times when some IRS agents still work remotely.

Please read this IRS FAQ for more information.

Please be patient, the situation will get better soon as some IRS agents are returning to their desks. You can check the status of your refund at this IRS web portal.