if last year's preparer did your return correctly box 9a on the k-1 is not passive. it's for portfolio capital losses. thus the capital loss should have gone to schedule D line 12 without limitation. if your 2020 capital losses exceeded your capital gains on schedule D what you have is a capital loss carryover. line 16 of schedule D would show the loss. your carryover would be reduced by line 22
there can be passive capital losses but the k-1 you got should have reported them on line 11
if an amount is showing up in part 1 of form 4797 it's been used and there is no longer any carryover. however, that loss can convert to a net operating loss if your other net income was insufficient to absorb the loss. we can't see last year's return so we can't be sure of any carryovers to 2021