I know it isn't an investment, but in the last few years some "high risk" investment funds have appeared, and in them you can either lose it all or earn a lot of money.
Isn't this basically the same as gambling? Wouldn't it be faster to just deposit the amount in a casino? At least you'd be able to spend your earnings much sooner

Yes and no.Real investing is about lowering the risk with diversifying the accets.
Never keep all your eggs in one backet.
Real gambling is about waiting for the right time to play your cards and playing all in...
There's still no big difference with whatever method you are using, you can do all in or not, in the end you still rely on your luck, without luck you can never win despite of the hard work you will do. Considering it as an investment is a hard thing to do, but it's possible and doable if you have passion in gambling, with that you have to win most of the time so your winning rate will increase and you will be profitable.