Hard to see Bitcoin can be a passive income because it requires a good amount of coins without staking to centralized company. So, in order to be realistic, we should treat Bitcoin as a store of value rather than bringing passive income.
Others believe that future innovations on Layer 2 or new financial instruments might make it possible to earn from Bitcoin without giving up security.
It's already exist, you can earn some sats by offering your node as router in Lighting Network. Although, it's not profitable as much as staking in lending company.