Q. Can I claim the $600 on my 2021 tax return?
A. Yes. You can, and MUST, claim the entire carryover loss.
The alternate, and common, question, in this forum, is: can I save my carryover loss and use it in later years when it will be worth more. The answer is no. You must report the entire carryover loss, each year. If you are again limited to $3,000, you can and must carry the excess to 2022.
If you use Turbo Tax next year it should automatically carry it over for you. So you might not need to enter it next year.
The current year carryover loss from the prior year is on schedule D line 6 & 14.
On the income page The 2020 column shows the carryover to 2021 (not your current loss for 2020). Schedule D doesn't actually show the carryover amount. To find your Capital Loss Carryover amount you need to look at your return schedule D page 2. Line 16 will be your total loss and line 21 should be a max loss of 3,000. The difference between line 16 and 21 is the carryover loss for next year.
There is also a Carryover Worksheet showing the carryover from the prior year and the current amounts. Then there is also the Capital Loss Carry Forward worksheet showing the amount transferring over to next year.
In the Online version you have to save your return with all the worksheet as a pdf file to your computer to see the Capital Loss Carry Over and Carry Forward worksheets.
In the Desktop program you can go to Forms and find it in the list in the left column.
If you have a negative AGI or negative taxable income it will show up on 1040 BUT it won't reduce the carryover to the next year.