Technically, you could just convert your raster to polygon and use that as the clip shape, however, you'll get one polygon per separate pixel value blob (connected pixels with same value), so it could get quite complicated.
A more reasonable method would be to Create Constant Raster, with exactly same cell size, snap raster, processing extent, and coordinate reference system as the DEM. This will make one rectangular pixel value blob exactly the size of your DEM. Then, convert the constant raster to polygon.
