TL;DR: Nvidia's DLSS has multiple versions, ranging from 1.0.0 to 2.2.10. Regardless of this, game developers can update it, but that tends to take some time. However, DLSS client libraries have become available so users can update DLSS themselves, but only within the major version (e.g. DLSS 1.0 can be upgraded to 2.0).
It seems that for each new wave of games receiving DLSS, there's a new version of Nvidia's upscaling technology. For example, Doom Eternal features DLSS 2.1.66, Rainbow Six Siege has the 2.2.6 version, and Unreal Engine 5 comes with DLSS 2.2.9, but all of them should be upgradeable to the latest DLSS version... presumably the 2.2.10 found on Rust.
Users can wait for the developer to upgrade DLSS in upcoming game patches, but a manual upgrade is also possible. This was discovered by users who replaced the DLLs corresponding to the DLSS libraries located in the game's installation folders, potentially enabling newer features, image quality or performance improvements. To swap the files, you'll need to acquire the "nvngx_dlss.dll" for the version you want and replace it in the game's installation folder. A quick Google search will lead to these .dll files, but it may be hard to pinpoint which are safe to download.
To help with this task, TechPowerUp created a library of DLSS files so users can download the version they want with peace of mind. We trust TPU who say all files have been "hand-verified to be the unmodified originals."
The library currently contains 23 files, from which 18 are DLSS 2.0 files, and the other 5 are DLSS 1.0 files. The files range from DLSS 1.0.0 to 2.2.10. TechPowerUp expects to grow the library of files as new versions are launched.
Do note, DLSS 1.0 games can't be upgraded to DLSS 2.0 by simply replacing the file. Only the game developer can do a complete version upgrade, similar to how Remedy Entertainment did on Control.
In theory, each new version should be the same or superior to the former in terms of performance and image quality, but some users' reports suggest otherwise. Depending on the game and DLSS version, results will vary, so if you're into tweaking files and optimizations, you will have to try them all until you find the best suited to your game.