How does the Creation/Redemption process work for Leveraged ETFs (i.e UPRO) vs. Standard ETFs (i.e VOO)?

I'm trying to wrap my head around the plumbing of leveraged ETFs like UPRO.

For a standard ETF like VOO, the process is pretty straightforward. When there's excess demand, an AP buys the underlying shares of the S&P 500 in the open market, delivers that basket of physical stocks to Vanguard, and Vanguard gives them newly created VOO shares in return. When there's selling pressure, the reverse happens: the AP redeems VOO shares and gets the underlying basket of stocks back, which they can then liquidate. It’s an efficient, highly liquid process driven by arbitrage that keeps the ETF's price tightly bound to its NAV

UPRO doesn't hold 3x the liquid stock with margin; they use swap contracts and future for leverage. These swap contracts aren't readily available to trade. So how can anyone, APs or Upro provider Proshares, create new shares when there's a spike in demand or redeemnthem? How is the share price tracking its NAV?

Appreciate if someone can walk through a concrete example.