I suggest looking at some of Google's open sourced projects.

- Abseil: https://github.com/abseil/abseil-cpp https://cs.opensource.google/abseil

- Tensorflow: https://github.com/tensorflow/tensorflow/tree/master/tensorf... https://cs.opensource.google/tensorflow

- Chrome https://chromium.googlesource.com/chromium/src.git/+/refs/he... https://source.chromium.org/chromium

There is a very high bar for C++ code quality at Google, and also a published style / best practices guide as well as a code search engine to browse the code more easily.