Bitcoin is Bitcoin and there is no altcoin can become Bitcoin.

I never heard about flash bitcoins but you know there are many altcoins that use Bitcoin open source code and make their altcoins, name them as Bitcoin forks. Two most famous Bitcoin 'forks' are Bitcoin Cash and Bitcoin SV. They are all failed altcoins.

How many Bitcoin forks are there?

There are many tokens, Wrapped Bitcoin tokens and they are not Bitcoin. They are even worse than Bitcoin (Proof of Work) forks because Wrapped Bitcoin tokens are mintable and their token pegs can be lost (de-pegged).