It is possible to earn without any monetary Investment online but the amount that you will earn will be very small. In most cases you will be investing a lot of time but the actual monetary output will be very less.
To earn good, you have to invest both money and time.
Not really, if you have the skill, then with time, you could earn quite big. Look for sites that offer "beer money" through skills, such as app testing, surveys, etc. Most of them aren't really crypto related though tbh. There's also the well known swagbucks.
Often people search "how to earn free money" which is quite complicated IMO. Everyone want to earn some money from internet which is almost impossible if you are looking totally free. I have remembered a story long time ago in our country, there was a online survey and they have asked to participate on the survey in order to get mobile recharge (balance). So I go in deep to check what is that and eventually a message popped after complete survey and that is "Nothing is free on the world". So from there I have learnt it and never tried for free money. Either you should have best knowledge and time or you have to invest on some good platform (doesn't mean PONZI scheme). If you have good skill or knowledge then you have to spend time like you may work web development or design, then you may earn some money over internet. If you fund then you may start lending business even on the forum. So spending time on Airdrop or similar platform wouldn't give your cost of your time. Find some real earning source would be a wise decision. Besides that free earning method would led you to scam.
Most of the time, what free really means is you either getting scammed 90% of the time, or the free is something that is of pitiful amount that isn't really even worth our time. It's actually a lot better to just find works that are pretty simple, pay low, but are constant at the very least. Like those delivery jobs that you find online. Most of what we find for "free" on the internet is actually a gamble, and 99% of the time, you'd find yourself inside a scam already.