According to my personal experiences airdrops, bounty programs and participating in testnet can be profitable if you know how to find them. For example the: Haven1 Blockchain and Haven1 Testnet.
interesting,
https://www.haven1.org/join-testnet a good airdrop campaign can be very profitable also, like ARBParticipation in airdrop or similar bounty campaigns is not passive income. On the contrary, it is necessary to participate in 100 different campaigns/airdrops and only two or three will bring some profit. In other words, passive income means that it is something that you don't have special daily activities for, while airdrops most often require the fulfilment of occasional tasks, trading and similar.