[tialaramex]

Yes. If the only value the library brings to you is that it generates a particular object file, you can divorce that object file from your chosen language version entirely.

If you have libraries that you don't care if they're C or Pascal or a Lisp implemented in raw machine code, then this works just fine and you needn't care about Rust's editions feature. Rust will also cheerfully consume these libraries although of course everything about them is by definition Unsafe in Rust terms.

But most people want their C++ libraries to deliver a bit more than "Here is some machine code, and here are some symbol names that map to the machine code or to raw binary data". Like maybe they want to be able to implement an Interface the library describes, or they want to use a Concept the library names. You can't do those things using language-independent object files.

Rust library A, from edition 2021 can implement a Trait from library B (edition 2018) on its thin wrapper of a type from library C (edition 2015) and then you can consume the resulting type, with its trait implementation, from your Rust 2018 program.