Man, if BTC is an illusion, it can't be tradable and it won't have value.  
It is the fact that BTC is a digital coin and it has value. If it is only an illusion, no one wants to use BTC as a digital asset or a digital currency.
Do you have BTC? Or do you ever sell and buy it on an exchange? People around the world trade BTC on CEX, DEX, or even P2P. It is enough as an indicator that BTC really exists.