They can't tax you for bitcoins that you keep in a decentralized manner, for example, if you keep your bitcoins in custodial services, then it is obvious that you will be taxed if they have regulated cryptocurrencies and crypto-related services within your country, because regulated platforms and services are supposed to provide them with all the data of their users, which includes your finances and financial activities with the platforms which is what they use to tax you if you have crypto and have capital gains within the year.
Technically this is true when talking about depositories but when the process changes especially after holding and selling Bitcoins we have at any time then there will always be loopholes for taxes and governments always target this as one of their ways to profit.
We know bitcoin will always be tax free when we keep this until whenever it may be tax free but when there is a transaction especially when making this as fiat then this is the gap that can not be avoided.
So even though we try to avoid taxes in bitcoin but it will still exist only we can minimize in terms of tax expenditures for a certain period of time when we don't make any transactions.
