At least 500,000 Bitcoiners are competing for the 21 million Bitcoins.
It is likely that hardcore Bitcoiners have already acquired a significant portion of the available Bitcoin, so we can conservatively assume that at least 500,000 people have a deep understanding of Bitcoin and the Bitcoin network.
With each individual striving to acquire as much Bitcoin as possible, the numbers quickly become astronomical, even if we don't consider the Bitcoin that have been lost or the early adopters who hold large amounts of it.
Thus, while theoretically we are competing for 21 million Bitcoin, in reality there is likely much less available.
I say at least 500k assuming that nostr users understand deeply btc.