Including R.H. G's in bar 120, is definitely incorrect.
Urtext has, in bar 120, before the key change:
L.H. d# octave
R.H. d# octave + f##
After the key change:
L.H. Starting on Eb, chromatically ascending octaves only. No thirds.
R.H. Pedal point on the tonic (Eb). No G's.
The Urtext commentary (The 1988 Critical Report, by Edwald Zimmermann) does not address bar 120, so I believe the Schmidt Edition is in error.
I played this bar with and without the R.H. G's. It sounds far better without the mediant, IMO. When the third is included, the harmonics are dischordant.
p.s. Pedal points are usually on either the tonic, (as it is in this case) or on the dominant. In this case, given the chromatic L.H., a pedal point on both the tonic, (Eb) and the mediant, (G) is nonsensical.
Per Sapientiam Felicitas!