> Even if bounds checks were only active in debug builds

In MSVC or Clang, when compiled against the Microsoft C++ STL, they already are. So,

  auto x = std::vector{1, 2, 3, 4, 5};
  std::println("{}", x[5]);

throws a very specific exception at runtime under debug mode.

In fact on Windows, even the C runtime has debug checks. That's why there are four options to choose from when linking against the modern UCRT:

  /MT (static linking, no debug)
  /MTd (static linking, with debug)
  /MD (dynamic linking, no debug)
  /MDd (dynamic linking, with debug)

For what 'debug in the C runtime' entails, see this comment I made a while ago[1]. As I mentioned, Unix-likes have no equivalent; you get one libc, and if you want to statically link against it, you have to release your own source code because it's GPL. Not sure why people put up with it.

[1]: https://news.ycombinator.com/item?id=40361096