Fear of being robbed by the government is much greater than the fear of having assets that the government does not know about.
If you want to declare your holdings, you can do so in parts. Send a smaller amount to a new wallet and declare it. If asked for the source, you can say you mined it in the past when it was worth zero.
You are not legally required to remember all the wallets you have used in the past, so you can continue to declare other wallets in the future as you recall, you can say coins were sent to new wallet due to security reasons.
(This will only work with Monero.)
The government not knowing how much you have is the greatest power you hold over these crooks.
If fear is a factor in your finances, it's game over for you.