Uhm . You are aware that you can make a game that puts the player into doing outright criminal stuff? What happens inside a game world is fictional. So unless fictional gambling is illegal, I think you are safe.

You would have to basically not have a game but casino software and some form of payout to consider, if you need a gambling license/permission.

Games with those infamous loot  box mechanism or gachas are considered gambling in some places. Most of the time the age rating  for the game just goes up and it depends on specifics of the pay to win lottery and the country.

But if you can not spend nor earn real life money ... well, just go and browse some gambling games on itch for reference. You can try tags like gambling, poker or casino.

One could even consider most rogue like games as some sort of gambling.