This is outside of my normal area of expertise, but from what I gather, the total geothermal power output was around 14 GWH in 2017 [1], with an estimated maximum of 2TW possible worldwide if we develop every spot available [2].

It looks like the current estimates of baseline power lost through plate tectonics from the mantle are 35-47 TW, "from secular cooling, internal radioactivity, and core heatflow across its base" [3,4]. To bring these numbers into scale, there is approximately 173,000 TW of heat energy bombarding the earth [5]. I am not able to find estimates for the total thermal energy stored in all of the earth, as there is decent debate about what the inner 'layers' are made of; however, it seems doubtful that we are making a large impact even on localized regions with a max current output of 14 GW when compared to the 35 TW per year lost naturally.

[1] https://www.iea.org/topics/renewables/geothermal/

[2] https://en.wikipedia.org/wiki/Geothermal_power

[3] http://adsabs.harvard.edu/abs/2016AGUFMDI52A..02D

[4] https://www.quora.com/How-much-energy-is-stored-in-the-earth...

[5] https://en.wikipedia.org/wiki/Earth%27s_internal_heat_budget