what u mean POW over onion
stratum pools can operate over tor, vpn, clearnet , i2p or anything - depends on miner firmware or app linux torsocks can make most app route via onion
Discussion
i thought they implemented some kind of pow for spam protection of the onion network, but i cant find the source now.
trying the alpha release of june https://gitlab.torproject.org/tpo/core/tor/-/raw/tor-0.4.8.1-alpha/ChangeLog