the only capital loss eligible for carryback are from regulated future contract losses - section 1256 contracts (form 6781) but there are special rules that must be followed in calculating the amount of carryback. other than 1256 losses, no capital losses are eligible for carryback so if you saw that somewhere please post the link. if it a 1256 loss carryback you amend by reporting the carryback on form 6781 for 2021.
