So as the mainnet is already on, it is "too late" for qualifying to the "possible" airdrop?
No, not necessarily. Although it's impossible to know the requirements one has to meet if they ever do an airdrop, the logical thing to do here would be to use the zkSync bridge as well as some other services (I can't tell you which ones since I'm not that familiar with their ecosystem) and also make sure to use your non-custodial wallet for that instead of an exchange's address.