How can the government discover I own BTC, let's say I'm from Venezuela where crypto is banned, what they can do to discover and arrest me?
Bitcoin transactions are anonymous. As long as you don't reveal your identity, no one know you are a bitcoin holder.
For this purpose you have to buy bitcoin peer to peer from a person you trust. Never use exchanges that force you to verify your identity.
knowing government owns a lot of money. for sure they will hire the best IT in the world to trace your BTC.