there is a difference between bankrupt and worthless. the IRS position is that an investment has to be worthless to allow a write-off of your investment.
for 2021 you merely leave all the current year info blank. there is no way to report you did not receive a k-1. however, if no return was filed the IRS does not have a k-1 for you either so the current year numbers will match - nothing
if worthless in 2022 you would as you go through check the boxes Final K-1 and Partnership Discontinued in 2022. this should free up the suspended loss. you should be able to determine your remaining tax basis from the 2020 k-1 Part II schedule L - capital account. the tax rules for that year stated it had to be on the tax basis. so if it's positive that balance would be written off as a capital loss. if it's negative there will be reporting issues. that negative basis could be ordinary income, capital gain or a mixture.
