UST was an algorithmic "stable" coin. The too-little-too-late BTC backing was bolted on later and useless: after all, if your algorithm works, you don't need BTC backing. And if your algorithm does not work, then a little BTC backing will not keep you afloat.
This fUSD however, is an at minimum 150% "backed" stable coin. The backing is only in Bitcoin or Liquid-Bitcoin (LBTC?)
So it's a lot like DAI [1], only they are backed by multiple assets instead of only Bitcoin.