The Monero community spent a long time trying to find a “useful PoW” function. The problem is that most computations that are useful are not also easy to verify as correct. javascript optimization was one direction that got pursued pretty far.

But at the end of the day, a crypto that actually intends to withstand attacks from major governments requires a system that is decentralized, trustless, and verifiable, and the only solutions that have been found to date involve algorithms for which a GPU or even custom ASIC confers no significant advantage over a consumer-grade CPU.