The Digital Elevation Model files can be added as raster layers into the QGIS project. It means, that their customization is quite analog to the XYZ tiles for map canvas.
1. DOWNLOADING THE DEM FILES
At the very beginning, it’s worth listing the websites, from where the DEM files can be downloaded. Some websites require an account for downloading the data.
-> Search.earthdata.nasa.gov – in my opinion, the most informative source, which gives you a chance for downloading various DEM files from many sources. An example of how to do it has been described in this article.
-> https://earthexplorer.usgs.gov/ – similar service, which also requires setting up an account, but various data can be downloaded easily.
-> https://dwtkns.com/srtm30m/ – the SRTM1 Tile downloader, which serves I believe the quickest option for downloading the 1°×1° dimensions SRTM files.
->Portal.opentopography.org – another platform, from where you can download various SRTM files quickly.
2. BAND RENDERING