At least in Tuscany - where there is a cluster of geothermal power plants creating 1/3 of the region electricity (it should reach 40% in a few years) - they had to invent special filters to lower the emission of mercury and hydrogen sulfide https://www.enelgreenpower.com/stories/articles/2024/10/geot...

I don't know if it's "no footprint" at all. For what I know, which is not much, but just what a person living here might know, there's a footprint that can be somehow managed. But I'm not an engineer