Yes, you can complete and file the 2020 tax return using TurboTax. If you file now the tax return will just sit on the servers until the IRS pulls the tax returns off the servers and starts accepting or rejecting returns on February 12, 2021
Although TurboTax will be accepting some e-filed returns early they will NOT be e-filed to the IRS which will not process any return until they open for e-filing. TurboTax stores those returns filed early until the IRS opens for business, only then will you get an e-mail telling you if the return was accepted or rejected by the IRS.
Only the simplest returns can be transmitted to TurboTax early. Some forms will not be finalized until late Jan. and some later then that.
Why does TurboTax allow early filing? Because their competitors do - It is a marketing ploy.
Filing early with TurboTax before the IRS opens is a really BAD IDEA.
1) If you discover something that is wrong on your return, receive a W-2 that is different, receive some other tax document that was not on the return that you filed then there is NOTHING that you can do about it other than wait to see if the IRS accepts or rejects the return after they open. If rejected you can correct and file again, but if accepted then the only remedy is to amend which can take 4 months to process.
2) You must remember to check back after the IRS opens (or check for an e-mail) to confirm that the IRS has accepted or rejected the return. If rejected, then it was never filed at all and must be corrected and re-filed. Every year many taxpayers that file early, forget to check back and only discover months later that they never actually filed because if was rejected by the IRS but they had forgotten about checking back after filing with TurboTax.
3) While the IRS does conduct some per-opening polling tests and does accept some returns early, they will not process those until after the official opening. There is a reason to test and that is to discover any problems with it's systems. A couple of years ago a test went bad and several thousand "test" returns were lost. The IRS was able to recover those but it delayed refunds for some by months.
There is no real advantage to file before the IRS opens but there are several disadvantages to do so.