Most countries have a cap at 10,000 USD (or foreign currency equivalent) for undeclared amounts of cash or other monetary assets, as amounts larger than that have to be declared upon travel. Crypto (like BTC or Monero) isn’t counted since it’s not considered as “valid currency” by the world bank.
The limit not only applies to cash since they count any assets worth of value (gold, checks, bonds, jewelery, artworks, luxury goods, high end electronics, etc). since those have been used and exploited for laundering money, I guess. So, even if he has 500 Rolexes fitted into suitcases worth over $100,000 will that still be taken?
It’s like if some one has 800 Chanel Handbags & 200 Hermès watches and mens footwear combined totalling to $50,000 in value stuffed onto mutiple huge suitcases and attempts to travel with that since huge stacks of cash will be flagged, so accessories are used to bring in money.
In Europe it was mostly done because rich people would transfer huge sums of cash to tax havens (Luxemburg and Switzerland due banking secrecy back than) so they could hide their wealth from the tax offices. So they limited the maximum amount you could travel across borders with.