It used to unpeg frequently (though not as bad as this TerraUSD episode). The stability has increased and the yield has decreased; a lot (yearly yield was close to 30% at some points). My guess is that they figured out how to peg efficiently as they have maintained the peg through various brutal crypto dips. The market does seem to think so (hence the low yield).
USD doesn’t have a yield either, and if I wanted to refer to the yield you’re describing here, I’d refer to the specific instrument that generates the yield (eg government bonds of a particular duration) rather than the yield on the invested asset itself.
