What if instead of spending energy on compute, we just spend money instead? On the one hand, some people may be turned off by the idea of spending money, but on the other hand, the two are usually interchangeable unless you're stealing energy. Someone with a lot of money and no hardware or energy can purchase hardware and energy; someone with a lot of hardware and energy can sell the hardware and sell energy back to the grid to make money.

How do you suggest the people who are using Tor for anonymity pay money to use Tor? That might make sense for cryptocurrencies, but for Tor I think it's unusable.

I believe this could be done using zero knowledge proofs, ala tornado cash (which I'm not familiar with in practice, but I've read the algorithms behind it). You'd need some service that produces zero knowledge proofs that someone sent some funds to the service, and got their slot in return. Put down your pitchfork, but I think this would essentially be an NFT backed by a ZK-snark.

The goal with Tor is to preserve privacy. Payment systems come with significant legal and regulatory overhead, KYC and AML, etc. That introduces significant privacy risk. Meanwhile PoW just requires owning a computing device.