Free Airdrops can certainly be a scam... perfect example: OTHO

Everything looked legit... got free tokens and then tokens started to be traded on a DEX.

They promoted what was going to be monthly HODLer airdrops after the initial airdrop, with a tiered structure - the more you owned, the bigger the slice of the next airdrop, so people subsequently were incentivised to go and buy tokens on the DEX to reach a higher tier.

subsequent airdrops never happened.

It was simply an elaborate plan to get a quick buck - it was the project team selling the tokens on the DEX to all the people looking to top up, and then they vanished.