The humidity slider works in msfs-2020 whereas it does not work in msfs-2024 (see report Humidity slider in custom weather not working)
What is saying @WeamDreaver is that the humidity slider in msfs-2020 does not have the same impact on the visibility than the aerosol slider had when the sim was released. The aerosol slider has been replaced by the humidity one in a later sim update.
See related topic: Where is the Aerosol Density slider gone?