The best way to earn passive income in cryptocurrency is to learn trading. Through trading can can earn 10 - 20 percent profit on your Investment. Airdrop and bounty can't do this for you. You can aswell subscribe to crypto job portals for community management and content curation jobs
airdrop and bounty can be said to be active income, not passive income. where we get money from doing a certain job and we will get paid, if we don't do anything we won't get anything.
I think that investment and crypto trading are the most suitable for our passive income, because we can do it anywhere, even if we get profits we can invest for more assets.