First of all, tax avoidance is not illegal, tax evasion is.
To even have a slight chance of getting any valuable advice here, you'd have to be more specific and state what's your current tax residency and include more details on how you acquired those 10 bitcoins.
In vast majority of western countries, simply owning 10 bitcoins is not something you would have to declare at all. You would have to declare and pay tax on it when you exchange it for something (e.g. fiat, goods, and sometimes, but not always - other cryptos) and make a profit on that trade.
I think this sums it up, correctly. Since I became interested in the subject I see that there are several forms of tax avoidance, legal as you rightly point out. One of the ones I have seen most mentioned is the creation and sale of NFTs. It seems that cryptocurrencies open a whole new world for tax avoidance, and I am surprised that it has not been discussed more in the forum.