My understanding of proof of work is that basically (miners/CPUs provide power to write transactions on the blockchain) whereas Proof of stake (is when we hold a certain currency and lock it into the systemso liquidity increases).Please correct me if im wrong.
Also why is it that only some coins can be staked?What are the conditions for a coin to be eligible to be staked?
And why are the returns on staking different on different exchanges?Is it simply due to difference in commission ,as logically the return on staking should be universally same depending upon the lock in period?
Your basic idea is correct, only difference is it's not about holding a currency, it's about giving it in to become a validator for that protocol, there are no such conditions, basically, whenever any cryptocurrency is created the developers create a protocol for the currency and that protocol would basically decide the mechanism of transactions in that coin, Bitcoin was developed as a proof of work currency which means you can't stake in it, while other currencies like BNB, SOL are created on the PoS protocol which means transactions are confirmed by validators and not miners. Basically, these are two different mechanisms on which different coin runs, you can't stake POW tokens and similarly, you can't mine PoS tokens.