I cannot remember if someone became a millionaire by doing an airdrop or bounty. Recently some people have made huge sums of money from airdrop like arbitrum and optimism but bounty work is not that profitable. I have seen people earn a maximum of a few thousand dollars from doing an altcoin campaign which was in the last bull run. This season, there aren't too many good projects in the altcoin bounty section that can give you even a few hundred dollars. The new project is not that interested in bitcointalk forum any more.
I can't remember if there were any one wallet millionaires with any airdrop, but many people got them with several wallets, and several different airdrops to different wallets. So i am certain there are some airdrop hunters who got in just by doing one with several wallets. I mean if there wouldn't be insiders who knew the requirements on how to get maximum amount and didn't use hundreds of wallets for themselves i would be very surprised.
And even if you didn't have insider access, there has been so many of them and selling them at the right time would have been worth a lot. Just holding an bored ape would have got you a lot of airdrops, and some people were holding several.