Slope Analysis/Reclassify from a DEM in QGIS 3 (in degrees/percentage)

Reclassification of a Slope/Raster in QGIS 3
1. At first load your DEM Raster to Qgis canvas/screen,
2. If your Input DEM Raster is on 'Degree/WGS_1984' then,
Reproject your DEM Raster layer's EPSG from Geographic CRS 'Degree/WGS_1984' to
Projected CRS 'Transverse_Mercator/WGS_1984_UTM_Zone_..N'
#[Raster-Projections-Warp 'reproject']

3. Now, goto Raster-Analysis-Slope,

4. On processing toolbox, type reclass and select 'Reclassify by table',

5. If you want to vectorize that classified slope then go to Raster-conversion-Raster to Vector

To download Processing Algorithms (tools for automation):
1. For Projected DEM: https://drive.google.com/file/d/1PBRy...
2. For Geographic (WGS DEM):
https://drive.google.com/file/d/1dyjy...