@jerryrs
Same boat as you, no actual trades just the reported "proceeds". I just bit the bullet and entered all the info. Took about an hour+ after I made a spreadsheet to calculate my cost on each individual entry. Saved an entire $7 in taxes.
You need this file to do the calculation, plus the pdf that covers the year(s) of your purchases:
https://grayscale.com/wp-content/uploads/2022/01/Grayscale-BTC-Annual-Reporting-12.31.21-Final.pdf
