In short, BTC can be said to challenge the global monetary system.
Bitcoin was not created to confront or challenge the monetary system, it was created to be an alternative, but that goal has also failed as it is only used as a speculative asset these days.
Bitcoin is a speculative asset like stocks, or some people use it as a store of value like gold, so how can it challenge the global monetary system? Bitcoin will not change or affect the current monetary system, nor will the fiat currency system face any problems just because of the existence of bitcoin.
People turn to bitcoin simply because it is a potential asset and has the opportunity to bring higher returns than traditional investment assets such as stocks, gold, real estate.