Ask where the money comes from before anything else. A token backed by short-term government debt pays roughly the policy rate and carries issuer and custody risk. One that lends reserves out carries credit risk. One that runs a basis trade, holding spot and shorting perpetual-futures to harvest funding-rate, carries market and exchange risk.
That last design is the least like cash. It earns while funding is positive and loses when funding turns negative for a sustained period, and it depends on the venues holding the short staying solvent. It can work, and it is a leveraged trading strategy wearing a stablecoin's clothing.
A rate much above what Treasury bills pay is not free money, it is compensation for a risk someone has decided not to emphasise. terra-ust-collapse is the canonical example of a subsidised rate that ended at zero.
Related: real-yield, basis-crypto, funding-rate, terra-ust-collapse