DEM is used to produce Slope raster. I use Snap raster but it does not work. Based on some posts, I uncheck background processing of geoprocessing but it did not make difference. Both the input and out are in the same coordinate system.
I would typically use the snap raster setting when processing rasters which have come from different sources to ensure the correct alignment, e.g. a raster DEM and a rasterized polygon boundary which I want to use for masking. The original polygon may have had the same coordinate system but it it will almost certainly have a different spatial extent. This is why you need to align the rasters. Snap Raster setting would ensure the rasterized boundary aligns to the DEM.
Your slope raster is being directly generated from the DEM so there is no alignment issue.