What type of LLC?  Single member unincorporated.  Single member incorporated as a S Corp.  Multi-member Partnership?

To do a 2020 return you need to buy the Desktop download program.  Either a personal program or the small business program depending on what kind of LLC you have.  Is it a Single Member LLC?  Is it an S Corp?  You might need to file it on Schedule C in your personal 1040 return.  Did you file a 2020 personal return?  

Sorry online is only for 2021 returns.  it's too,late to start a 2020 online return or use the mobile app, either on Turbo Tax or the IRS.

To do a prior year return you have to buy the Desktop program here,

https://turbotax.intuit.com/personal-taxes/past-years-products/

You will need a full Windows or Mac to install it on.

If this is a multi-member LLC, then seek professional help yesterday, if not sooner. Late filing penalties are high, You can almost double that penalty if your state taxes personal income. See https://www.irs.gov/payments/failure-to-file-penalty for information. I don't know if the provided information applies to your specific and explicit situation, or not.

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@Carl wrote:

If this is a multi-member LLC, then seek professional help yesterday, if not sooner. Late filing penalties are high,

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The late filing penalties for a multi-member LLC (taxed as a partnership) can be found at the link below.

https://www.irs.gov/instructions/i1065#en_US_2021_publink11392vd0e1221