Of the systems listed in the paper, the only one I'd really heard of was BrightID, and it still seems like potentially the best. The FAQ on their website is a good introduction[0], but the paper seems rightly cautious:

"To control for Sybil attacks BrightID runs GroupSybilRank, a modification of the SybilRank algorithm, to estimate the anti-Sybil score of the network participants based on affinity between groups. Proposed to be used as the official BrightID anti-sybil algorithm, the effectiveness of this algorithm in the presence of multiple attack vectors, remains to be proved."

Unfortunately, just proving personhood is only the first step in deciding someone's reputation, but it seems like a good basis to build some proper decentralized trust systems from, for example [1].

[0] https://www.brightid.org/faq

[1] https://adecentralizedworld.com/2020/06/a-trust-and-moderati...