Yes, it's possible to make a stable coin without even real back up of fiat.
But those type of stable coins are likely to get exposed when someone audits and look at its history. Well, those that are backed for real, they're audited and said that they've been registered and verified that they've got an actual backing fiat.
This is what's scary in stable coins lately, even they're reputable, it cannot be removed in the minds of everyone on what happened to UST.
UST is algo-based and no backing of actual fiat. So for me, this is more risky as compared to stablecoin pegged at fiat. As UST crumbles, it goes to show that algo-based stablecoin is hard to trust your hard-earned savings. But it may be the same with stablecoin backed by real fiat, because if it is centralized, the team has the power to manipulate their code. But the crash may not be the same as algo-based. Bottomline, it is hard to trust stablecoin whether it is algo-based or fiat-based, because the future of the coin depends on the dev team themselves.