I know blockchain game which you can play and earn cryptocurrency is not free Smiley. For example, Cryptokitties is the only blockchain game that I know and it's not free Smiley. You still have to invest ETH to play although it's just a little. But I think it's worth to try cause as I know there are so many guys earned thousands dollars from blockchain games.
it does need to be Blockchain based game to enjoy and make money specially now that NFT games are circling the community .
there are many options now in which some does not require capital but only Time, Gadget and Internet as you can grind to generate income.
Axie Infinity and Even Mir4 that is in demand nowadays.
so while Cryptokitties has already passed its time now try other games and you might get some funds while playing .