Yes. Exactly.

Older stuff here: https://github.com/ValveSoftware/steam-runtime

Newer stuff here: https://gitlab.steamos.cloud/steamrt

The dev guide within that gitlab repo confirms that it can be used sans Steam: https://gitlab.steamos.cloud/steamrt/steam-runtime-tools/-/blob/main/docs/slr-for-game-developers.md

This applies to the new runtime as well: https://gitlab.steamos.cloud/steamrt/steamrt4/platform