Wrong. You're confusing tokens. I'm talking about UST, not USDT, they're completely different tokens on different blockchains. USDT is backed with what you said, UST is an algorithmic stable coin.
DAI is backed by other cryptos (mostly ETH), but also other stable coins such as USDC.
USDC is backed by USD and US bonds
BUSD is backed by USD
USDT is backed by USD (less than 4%), corporate and government bonds, and other commercial papers. USDT is the least transparent.