the section you quote has NOTHING to do with crypto
"digital currencies" are things like a coinbase DOLLAR balance, or a loyalty card DOLLAR balance or a paypal DOLLAR balance... not crypto
The fact that the bill specifically references tumblers (mixers) makes me wonder if that is the correct interpretation. Coin Center did put out a blog that suggested that the bill was largely redundant in regards to existing law. However, the blog also played up the worries around declaration and seizure of cryptocurrencies like Bitcoin:
Coin Center also honed in on fears that digital currency holdings could be subject to declaration and seizure at the US border, with Brito noting that, at present, the bill calls for a report on how customs agents might approach this process.
https://www.coindesk.com/coin-center-us-senates-digital-currency-bill-is-counterproductive/Its kind of a double edged sword in that respect isn't it? By requiring declaration the government implicitly endorses bitcoin as a legitimate store of wealth. Right now anyone that knows even a little about bitcoin knows how to move coins around as they travel.