Nowadays the heat in my apartment is mainly geothermal (The district heating network in my neighborhood has been converted to geothermal energy over the past 10 years.)
"Medium-deep geothermal resources in the Molasse Basin: A geological, techno-economic, and ecological study of large-scale heat pump integration"
https://www.sciencedirect.com/science/article/pii/S096014812...
Tapping a geothermal aquifer system is much easier than to get useful quantities of heat from dry rock, because in most places the thermal conductivity of rock is very low.
"The enthusiasm in the research community is justified by the vast extent of the energy supply and the low environmental impact of the method, however significant breakthroughs will be required to make this a commercial energy resource."
https://en.wikipedia.org/wiki/Hot_dry_rock_geothermal_energy