You're clobbering together a bunch of different stuff and not making a ton of sense. C and C++ are very different languages, and that's especially true when doing interop with them from other languages.
For C-based libraries, P/invoking is trivial in C# and has been around forever. And it's cross-platform, working identically on Linux and macOS. I have no idea how you can say ".Net hasn’t ever really had that kind of focus" when it's been a core part of .NET from the start, and .NET relies on P/Invoke to do everything. Go look at all the DllImport() statements in the .NET reference source. Rust FFI is nearly identical in implementation to C#. Go has a slightly different implementation with the CGO module, but whatever, it's close enough. Just step back and remember that, in general, calling into C code is trivial in every language, since it has to be: all these languages will eventually have to hit libc / user32.dll / whatever.
C++ is a totally different story. You can't work with C++ libraries with P/Invoke, that's true... But you also can't work with C++ libraries using Rust or Go, either. Nor Python, Java, Javascript, or really any other popular cross-platform language.
C++ dynamic libraries are really challenging to call into for a variety of reasons. Virtual functions, multiple inheritance, RTTI, name-mangling, struct/class layout, vtable placement, ABI differences, runtimes, etc all make calling into precompiled C++ libraries a nightmare.
In fact, the only way I know of working with pre-compiled C++ libraries is with languages that target specific operating system / compiler collections. E.g., Objective-C++/Swift from Apple, and C++/CLI from Microsoft. These are obviously not cross-platform solutions, since they depend on knowing the exact compiler configuration used to build those libraries in the first place.
For every other language, you either need to manually build C shim libs that you can call into using the C-based approach above, or if you have access to the C++ source code, creating wrappers around it and building it into a module (for example, using pybind11 in Python).
For C-based libraries, P/invoking is trivial in C# and has been around forever. And it's cross-platform, working identically on Linux and macOS. I have no idea how you can say ".Net hasn’t ever really had that kind of focus" when it's been a core part of .NET from the start, and .NET relies on P/Invoke to do everything. Go look at all the DllImport() statements in the .NET reference source. Rust FFI is nearly identical in implementation to C#. Go has a slightly different implementation with the CGO module, but whatever, it's close enough. Just step back and remember that, in general, calling into C code is trivial in every language, since it has to be: all these languages will eventually have to hit libc / user32.dll / whatever.
C++ is a totally different story. You can't work with C++ libraries with P/Invoke, that's true... But you also can't work with C++ libraries using Rust or Go, either. Nor Python, Java, Javascript, or really any other popular cross-platform language.
C++ dynamic libraries are really challenging to call into for a variety of reasons. Virtual functions, multiple inheritance, RTTI, name-mangling, struct/class layout, vtable placement, ABI differences, runtimes, etc all make calling into precompiled C++ libraries a nightmare.
In fact, the only way I know of working with pre-compiled C++ libraries is with languages that target specific operating system / compiler collections. E.g., Objective-C++/Swift from Apple, and C++/CLI from Microsoft. These are obviously not cross-platform solutions, since they depend on knowing the exact compiler configuration used to build those libraries in the first place.
For every other language, you either need to manually build C shim libs that you can call into using the C-based approach above, or if you have access to the C++ source code, creating wrappers around it and building it into a module (for example, using pybind11 in Python).