sqlite/sqlite is the official Git mirror of the SQLite database engine source tree. It holds the engine's full source code, test code and some documentation, and GitHub lists C as the primary development language.
The important point is that the official development history lives outside GitHub. The SQLite sources are managed with Fossil (a version control tool), and this repository is only a Git mirror of that history. The README covers how to build on Unix-like systems and on Windows, how the source tree is laid out, and how to check that the code matches the actual SQLite code. To grasp the source structure and follow the build procedure, starting from this repository is a reasonable path. The repository was created on March 18, 2019 and has 10740 stars.
That said, this repository alone does not settle the matter. No releases are registered, so no per-version change history or release notes are given. From this mirror alone it is hard to confirm when a particular version changed what. The license is shown on GitHub only as NOASSERTION, so no clear terms of use are stated. Of the evaluation scores on a 10-point scale, the novelty, technology and quality items are empty, and only the momentum score comes out, low at 4.0. This repository can serve as a route for reading the source and checking the build procedure, but to judge version-level changes and usage terms, it is better to consult the official release distributions and the official Fossil repository as well.