From Rust 1.100.0, you can no longer install the Rust compiler on a 32-bit Windows machine, but you can still build 32-bit Windows programs from a 64-bit machine.
Only 6.4% as many people download the `i686-pc-windows-msvc` compiler as its standard library, per RFC 3999, so the target is used mostly as a build destination.
The standard library for both i686 Windows targets stays prebuilt, and `i686-pc-windows-msvc` stays in the project's CI.
You are affected only if a 32-bit Windows computer runs `rustc` or `cargo`, which a two-line host check will tell you.