I moved back to the UK in August. Do I still need to file? Can I still file using Turbo Tax?

[Critter-3]

Yes you need to file ... and to buy  the TT program directly from TT you must have a US Credit Card with a US billing address.   Other place who sell the program may have different requirements.

If you qualify  AND   if you wait until mid January  THEN you can use one of  the IRS FREE FILE options to file a fed & state return for free ... but you must be patient.    https://www.irs.gov/filing/free-file-do-your-federal-taxes-for-free

IRS Free File: Closed until January 2021

IRS Free File is closed for the 2020 tax season. Check back in January for Filing Season 2021 opening details.

For Filing Season 2021, you must make $72,000 or below to use IRS Free File partner offers.

[rjs]

Are you a U.S. citizen? resident alien? nonresident alien?

Did you work in the U.S. in 2020 before you left?

Did you have any income from U.S. sources in 2020? If so, what kind of income?