Clustering 30m pixels into 120m pixels, fishnet using QGIS?

So I found a second best solution to the question asked above.

Using R one can aggregate raster pixels by a factor, in my case a factor of 4, and then export the newly created raster. This raster can subsequently be used in QGIS.

Please note that this can take a very long time. My raster is a 80000*40000 pixels so aggregation takes about one hour per raster file.

library(raster)
DEM <- raster("/Users/.../input.tif")
dem_low <- aggregate(DEM, fact = 4, fun = mean)
writeRaster(dem_low,'/Users/output.tif',options=c('TFW=YES'))
rm(DEM,dem_low)