If the coins are on Bitcoin main blockchain, they are Bitcoin. Anything else is not.
And from here the list of "fake" coins can get big:
* Bitcoin forks, misleading because they contain "Bitcoin" in their name and some even advertised as the true bitcoin. The list is big, most known are BCH and BSV.
* Bitcoin testnet coins. Bitcoin testnet is for testing, so those coins don't hold value. Testnet blockchain is also reset from time to time and the very old coins cannot be used.
* "Home brew". Anybody can make his own blockchain, the source code is public, and can have his own Bitcoin at home. Of course the chance to stumble over such Bitcoin is slim (there were some time ago discussions about a hypothetical scam based on such coins).
* Tokens. Various altcoin blockchains offer the possibility to create tokens. Ethereum and Waves are 2 such networks, but the list is big. The tokens don't have their own blockchain and the tx fees are (usually?) in the "parent" coin. Tokens can have basically almost any name, so tokens called Bitcoin or with Bitcoin in their name can exist. Those are, again, not Bitcoin.