I do not know how Coinbase transactions will work. I am just a user of Turbo Tax. I assume there is a csv file with all crypto transactions and there is a PDF file (1099).
In the Cypto section, instead of uploading the CSV file or connecting with coinbase or Robinhood, there is an option stating if you want to enter the crypto transactions manually. Then it says if you have more than four (or five, I do not remember exactly) transactions. If you say yes, then you can enter the information on the last page of the PDF. On the last page of the PDF I have "total crypto Proceeds" and "Cost or Other Basis". If you enter them on Turbo Tax, it will subtract Cost basis from total crypto Proceeds to compute the net gain. Then you will have the option to upload the PDF file. (If you uploaded CSV earlier, you will see that the net gain/loss is the same as the new entry. Please make sure to remove the previous entry that was automatically retrieved from CSV or by connecting with coinbase.)
Somewhere it asked be to select one of several types of transactions. I only had a type involving "SHORT TERM TRANSACTIONS FOR NONCOVERED TAX LOTS", or it was something like Transactions that were not reported to IRS by the crypto brokerage.
Please note that I do not remember the exact steps because I am just a Turbo Tax user trying to explain things based on only this year's experience. I did not have much crypto transactions in the previous years, so I never faced this issue.
