JOSM, relief hillshade layers worlwide.

Tried to find a worldwide one
Are there wms or wmts or tms layers to use?

IMHO not out of the box.

did you try some searching for “srtm qgis” or “aster qgis”? … Maybe there are some TMS sources mentioned.

Looked for something, but there is so much written, today on the internet, you can not find the tree in the forest, easy, it is a science, knowing where to read it. Searching is sometimes a lucky guess.

There are layer that are cooked in, but stand alone, which we can use with a little transparent.

Hoped for a hint, easy to use layer.

Finally you can try to ask on directly,

or do some searching there for SRTM or Relief or Terrain or Aster or DEM