The legislation of several countries obliges you to declare the mere possession of cryptocurrencies.
Those laws are still being debated, as far as I can tell. No (reasonable) country can punish you for holding bitcoin you didn't declare for 10 years when they are only just making it mandatory to declare it now.
Still, I assume they will want a simple statement of "I own 1 BTC", as opposed to wanting you to report individual wallets or addresses, given that lots of people holding their coins on custodial exchanges and wallets and so wouldn't be able to provide such information. So there is a still a significant privacy improvement from government surveillance (not to mention surveillance by third parties) by using non-KYC peer to peer trading over centralized exchanges.
Even if they don't have an explicit law requiring citizens to disclose their Bitcoin holdings, wealth tax does not usually exceed $1M by much. So you should declare your holdings when you exceed that figure.
So how does that work in practice? You take the average value of bitcoin over the year? Or you take the spot value of bitcoin at the end of year?