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?
I think as long as you use centralized exchanges to trade your bitcoin, highly likely you could be traced.
As long as you don't trade, and have you btc stored at your wallet which you control with private key, tracing you doesn't become that easy.
Still there are numerous ways for government to get whom or what they want, but for us - ordinary people there should be not much to worry about.
As even in Venezuela government has some greater tasks to do, as to trace every single crypto owner.