If your government bans Bitcoin and the police find Bitcoin in a citizen's possession, the following mechanisms are available. It's virtually impossible to confiscate Bitcoin unless the citizen hands over the private key. Therefore, the court can seize or confiscate the citizen's property worth that amount. If the citizen has no property, the government can ban them from leaving the country until they pay the debt, as well as other adverse legal consequences.
In some nations, governments through police can enter citizen houses and do their 'dirty jobs' for finding things they need. Like if they know you have bitcoins, and you broke some kinds of laws, they will enter your house and find 'evidence' while who knows what will they do if they find your bitcoin private keys, wallets and so on. In such nations, the best practice is don't let governments knowing about your Bitcoin and cryptocurrency related activities. Don't do anything stupid that can bring them to your home, as if it happens, you will lose your bitcoins.
People who are living in nations with Illegal, Allegal or Unknow legality of Bitcoin and cryptocurrency have to practice more carefully than people who are living in nations where the legality of Bitcoin & cryptocurrency is legal.
https://newhedge.io/terminal/bitcoin/legality-map