Broadly speaking, authorities looking for money laundering focus on transactions not on assets. It is generally much more interesting to look at where the money is moving from and to than at the actual monetary amounts.
If you're looking for money laundering, someone walking into a bank with $10,000 in cash is suspicious because you have no idea where that money came from. Someone transferring $100,000 from their brokerage account to their checking account is not. Both the broker and the bank know the customer and the government knows that both sides have reasonably strict controls in place to prevent money laundering. If you make a huge gain in your brokerage account, that isn't indicative of money laundering (it could be indicative of other financial crimes like insider trading). Someone transferring $10,000 from some fly-by-night crypto exchange the government has never heard of operating out of a country whose regulatory environment is known to be problematic would likely produce a similar level of suspicion to walking into the bank with that same amount of cash.
Different governments, of course, have different protocols for how regulated entities like banks need to screen customers and to alert authorities to suspicious transactions in a way that balances privacy and security. But any country that is part of the established Western financial system will have a system by which regulated entities like banks and brokers report suspicious transactions for the government to investigate. If there were $50 M in transactions from the suspicious crypto exchange to your bank account during the year, the bank would have filed suspicious activity reports with the Swiss government long before tax time and the authorities would be able to investigate whether you were a lucky speculator, a money launderer, or something else. They're not going to wait for tax time to start investigating.