How if I buy bitcoin from someone who can help people have bitcoin without going to the exchanges (cex or dex)?
If you buy through a peer to peer exchange, and if you never hand over KYC or any other details, and if you use a payment method which isn't linked to your identity, and you do all that over Tor, and you receive the bitcoin to a brand new address, and you never link those coins to other bitcoin you own, then you can be relatively sure that the government don't know you have bitcoin. But simply saying that the government don't know if you buy bitcoin is wrong. Centralized exchanges freely share information with governments, and governments are spending millions of dollars on blockchain analysis to track down bitcoin owners.
I buy bitcoin from a local seller that I know most and have trusty and he already helps many local people who want to buy bitcoin without using an exchange. Does the government know the bitcoin transaction? I doubt that ;P
The government and the banks only know the cash flow of the money from the transaction. But for the bitcoin flow for the transaction, the government can only trace the flow of the transaction even if I use the same wallet address. I hope you understand what I mean.