You'll find several opportunities other than mining which actually, in my opinion, isn't really passive, as any miner can tell you, it's almost a full time job really because you always have to monitor and maintain. First thing that comes to mind is investment in casino bankrolls, there are several which offer the chance.
Others like BitDice (in my signature) you can buy the native tokens that are linked to profit sharing every quarter. That's truly passive but of course carries a risk like all investments.
That is usually the big thing which matter the most. There is no investment at all that does not come with a risk, even outside cryptocurrency, but this you have mentioned is not a bad idea at all, as I am getting to even come across it for the first time. I never knew Bit Dice had a native token for profit sharing purpose.
However, there are some PoS tokens that one can get as well, which would keep giving you something substantial over time, if you really do not want to tie down your money into mining, and for what it is worth, in the long run, the chances of seeing the whole market doing well and then hitting some huge level is also a plus even if the OP peradventure decides to hold for the long term. That on its own is already an investment.