So it may be easier to fix things manually than rely on cargo fix.
imports_granularity = "Crate"
group_imports = "StdExternalCrate"
A new edition doesn't mean features are automatically stabilized.
I agree with these two specifically, it would be great to have them in stable. They're not yet though: https://github.com/rust-lang/rustfmt/issues/5083
Not that every compiler is up to date, but at very least clang, gcc and vc++ have already quite good coverage of C++20, and clang/vc++ modules mostly work, good enough that I only use modules in my hobby projects.
It starts by projects, companies, actually wanting to adopt new toolchains.