The whole point of opensource is making your source code public. Even if you can disable history viewing in GL, someone can still mirrors your repo and diff it for changes. The only way to not let people see changes is simply not open sourcing it.

Private submodule can help hiding some of your code and configurations, but this only helps hiding parts of the repo, including its history. You can’t preventing people measuring changes of your webpage once online as anyone can just archive it.