reproject and reduce like in Google Earth Engine but in R?

Question

I created 2 max_NDVI collections in Google Earth Engine, one from VIIRS and the other from MODIS. I reproject the VIIRS collection to 500m and then reduce it resolution.

//----------------------------------------------------------------------------------------------           
      // Get the NPP NDVI Decadic collection at MODIS scale and projection.
      var npp_pro = tnpp.first().projection();    
            
      var npp_resample = function(image){
        return image.reproject(npp_pro, null, 500) // insert here the desired scale in meters
        
        // Force the next reprojection to aggregate instead of resampling.
        .reduceResolution({
          reducer: ee.Reducer.mean(),
          maxPixels: 1024
        })
        .copyProperties(image);
      };
     
      var tnpp_resampled = tnpp .map(npp_resample);
//----------------------------------------------------------------------------------------------

Finally I have a collection of reprojected and reduced VIIRS images, which values are comparable with those of the MODIS product.

I'm trying to do the same thing using R. I can get both collections but I'm in trouble when I try the reprojection and reducing parts.