I didn't receive my Federal Tax returns and IRS website doesn't recognize my credentials. I received both state returns without any issues.

The refund amount will revert to 0 (zero) on the amended federal tax return when first starting to amend the federal return.  If you did not file the the Form 1040-X then the IRS would only have the original 2020 federal tax return that was filed.

Assuming you e-filed the federal and state tax returns and you received the state tax refund, the federal return was Accepted by the IRS.  A state return cannot be e-filed if the federal return has not been e-filed or Accepted by the IRS.

The IRS website for federal tax refunds has had multiple glitches this tax year.  Your federal tax return may be between stages so is not showing any information.

Once a tax return has been Accepted by the IRS or a State, TurboTax receives no further information concerning the tax return or the status of any tax refund.  

If accepted by the IRS use the federal tax refund website to check the refund status - https://www.irs.gov/refunds

After the tax return has been Accepted by the IRS (meaning only that they received the return) it will be in the Processing mode until the tax refund has been Approved and then an Issue Date will be available on the IRS website.
See this IRS website for federal tax refund FAQ's - https://www.irs.gov/refunds/tax-season-refund-frequently-asked-questions
If over 21 days since being Accepted by the IRS and the tax refund is still Processing you can call the IRS and speak with an IRS agent concerning your tax refund.
Call the IRS: 1-800-829-1040 hours 7 AM - 7 PM local time Monday-Friday
When calling the IRS do NOT choose the first option re: "Refund", or it will send you to an automated phone line.
So after first choosing your language, then do NOT choose Option 1 (refund info). Choose option 2 for "personal income tax" instead.
Then press 1 for "form, tax history, or payment".
Then press 3 "for all other questions."
Then press 2 "for all other questions."
- When it asks you to enter your SSN or EIN to access your account information, don't enter anything.
- After it asks twice, you will get another menu.

Press 2 for personal or individual tax questions.
Then press 4 for all other inquiries
It should then transfer you to an agent.

Stop looking at the Refund-O-Meter which reset to zero when you started the amendment.  Making changes in the program without  efiling or mailing them in means the IRS knows nothing of them.