I have unfiled tax returns from 2018 through 2024.

No.   Unfiled-----and prepared where?   Only a tax return prepared using TurboTax software can be filed via TurboTax.  And...only a 2024 return can be e-filed.

Any past year return can only be filed by mail.    The returns for 2023 back to 2018 can only be printed, signed and dated and mailed in their own separate envelopes to the IRS and/or states.

Any refunds for  years earlier than 2021 have been forfeited.   If you owe tax due for any of those years, you owe with late filing penalties and interest.

If you want to use TurboTax for some of them, you can purchase the TT software and use it on a full PC or Mac as far back as tax year 2021.

To file a return for a prior tax year

 If you need to prepare a return for 2021, 2022, or 2023  you can purchase and download desktop software to do it, then print, sign,  and mail the return(s)

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

You may also want to explore purchasing the software from various retailers such as Amazon, Costco, Best Buy, Walmart, Sam’s, etc.

Remember to prepare your state return as well—if you live in a state that has a state income tax.

https://ttlc.intuit.com/turbotax-support/en-us/help-article/state-taxes/contact-state-department-revenue/L9qVToi02_US_en_US?uid=m6e06um0

When you mail a tax return, you need to attach any documents showing tax withheld, such as your W-2’s or any 1099’s.  Use a mailing service that will track it, such as certified mail so you will know the IRS/state received the return.

Federal and state returns must be in separate envelopes and they are mailed to different addresses.  Read the mailing instructions that print with your tax return carefully so you mail them to the right addresses.

Refunds for tax years 2020 or earlier have been forfeited and will not be paid to you even if shown on the tax return form.  But if you owe tax due, you will still have to pay, and you will be billed later for the interest and penalties owed.  TurboTax will not calculate the penalties or  interest.   That will be done by the IRS/state after they receive your return with your payment of the tax due as shown on the tax form(s).