Why one coin can run on many different explorers platform. The specific example here is the BNB coin.
A coin can't run on a different blockchain, but a token(Wrapped BNB or BNB) is possible.
The problem is that BNB Token on ERC-20(Ethereum) only exists within Ethereum Ecosystem. And that is also applied on each network where BNB exists. The reason why BNB exists on many chains/networks is to fix some interoperability cases.
How is the total supply of BNB fixed when two different validators will have different total coin issuances. For example, currently BNB has a total supply of 160,000,000 BNB, how much is etherscan issuing and how much is bnbscan issuing and how is it related?
I believe the below reference is good for getting a grasp of how it works.
1.
What Are Wrapped Tokens?2.
What Is BNB?3.
What Is a Coin Burn?