Moving to PoS is a necessary but not sufficient criteria for reducing transaction fees. The Ethereum merge will reduce them slightly (as it will reduce the block time from 16 seconds to 12 seconds, or something like that) but it won't make any big difference. In the coming year, there probably will also be general ZK-rollups on Ethereum mainnet that will reduce transaction fees substantially. (You can already use ZK-rollups for some limited things like transactions, but not for arbitrary Ethereum operations.) Also, way out in the future, there will be data sharding which will reduce fees on mainnet significantly, look up "proto-danksharding".