Currently all the 1.85 images (https://hub.docker.com/_/rust/tags?name=1.85) are based on either Debian Bookworm or Bullseye.
Debian Trixie (stable release for approx the next 2 years) ships with 1.85 (https://packages.debian.org/source/stable/rustc, https://tracker.debian.org/pkg/rustc).
It would be useful to have Trixie based 1.85 container images available (eg, rust:1.85.0-slim-trixie) to match what Debian Stable ships with.