Hi i got a letter from the FTB, says I didnt file my tax returns for 2020. I did use the turbotax software, and I did file for it, have the filing in my computer?

Does the letter say you did not file----or does it say you did not pay your tax due?   Your only proof that you paid your tax due would be your own bank or credit card records.

Does it show that your 2020 tax return was accepted?  

perhaps you selected mailing for Ca. Turbotax does not mail your return. Not sure what you mean by not uploaded in the Turbotax website