But there's no guarantee to earn from airdrops because most of them are just scam hence it's not a reliable way to gain.
Yes, it is free but it's not that really guaranteed at all. You're likely ended being hopeless and wasting your time and energy on it if done these days.
And much worse, if you become a victim of those airdrops that would ask for a little amount of reasoning out that they need it for the transaction fees so that they'll happen to send those token rewards that you're eligible to.
Nowadays if you like to earn in crypto, skills and effort are necessary.
Not only in crypto but in real life and that's to have a real job and make money from it through salary and then invest it in bitcoin.