Bitcoin's decentralization is not controlled by the government and central banks, and it can be used to conduct free transactions without the government's knowledge and taxation.
Decentralization in essence means that a central authority or a system doesn't have the power to control how something works or what direction it will take in the future. Bitcoin transactions, like the majority of other crypto transactions, are not free. You don't pay a centralized entity, but you need to pay the miner to include your transaction in their block.
Depending on what services you use, your government could have the mechanisms to keep track of your crypto activities. If you use centralized exchanges where you have performed KYC, they could be cooperating with your government and share information about the citizens who transact on their platforms. Or a government agency could contact the exchange and request them to hand over information about a certain individual who they suspect might be laundering money or avoiding to pay their taxes.
Yes, as Bitcoin becomes more and more influential in the world. The government will definitely try to control Bitcoin in various ways. Probably the main method is to tax people who own Bitcoin. However, Bitcoin is in a completely independent and completely free economic system. Without the existing monetary system, it is difficult for the government to intervene in the independent operation of the Bitcoin network through administrative power. In this way, each of us is given real freedom to manage our property. The Bitcoin consensus will become stronger and stronger, which will force government agencies to adapt to the development of Bitcoin. Eventually, a new human civilization will be built with Bitcoin as the center.