I’m afraid the question doesn’t really make sense conceptually.
Cesium is an interactive 3D globe tool, rendered with WebGL. It requires an HTML
<canvas> tag, which then uses the client’s own 3D graphics capabilities to draw frames directly. This requires JS to create the WebGL context and do all the drawing.
“Server-side rendering” as a term normally refers to the process of generating HTML tags in a document and send them to the browser.
You could have the server write out a
<canvas> tag, but that cannot do any of the 3D drawing itself.
Beyond that, what would the server “render” here even if it could actually spin up Cesium? A single static frame and send it back as an
<img> tag? I suppose you could maybe do some kind of streaming video thing, but that would be a pretty huge undertaking.