Over the history of a given Fedora version, Fedora will often release multiple updates to the same package (for example, kernels, but there are many others). When it does this, the older package wind up being removed from the updates repository and are no longer readily available through mechanisms like 'dnf list --showduplicates <package>'. For a long time I used dnf's 'local' plugin to maintain a local archive of all packages I'd updated, so I could easily revert, but it turns out that as of Fedora 41's change to dnf5 (dnf version 5), that plugin is not available (presumably it hasn't been ported to dnf5, and may never be). So I decided to look into my other options for retrieving and installing older versions of packages, in case the most recent version has a bug that affects me (which has happened).

Before I take everyone on a long yak-shaving expedition, the simplest and best answer is to install the 'fedora-repos-archive' package, which installs an additional Fedora repository that has those replaced updates. After installing it, I suggest that you edit /etc/yum.repos.d/fedora-updates-archive.repo to disable it by default, which will save you time, bandwidth, and possibly aggravation. Then when you really want to see all possible versions of, say, Rust, you can do:

dnf list --showduplicates --enablerepo=updates-archive rust

You can then use 'dnf downgrade ...' as appropriate.

(Like the other Fedora repositories, updates-archive automatically knows your release version and picks packages from it. I think you can change this a bit with '--releasever=<NN>', but I'm not sure how deep the archive is.)

The other approach is to use Fedora Bodhi (also) and Fedora Koji (also) to fetch the packages for older builds, in much the same way as you can use Bodhi (and Koji) to fetch new builds that aren't in the updates or updates-testing repository yet. To start with, we're going to need to find out what's available. I think this can be done through either Bodhi or Koji, although Koji is presumably more authoritative. Let's do this for Rust in Fedora 41:

bodhi updates query --packages rust --releases f41
koji list-builds --state COMPLETE --no-draft --package rust --pattern '*.fc41'

Note that both of these listings are going to include package versions that were never released as updates for various reasons, and also versions built for the pre-release Fedora 41. Although Koji has a 'f41-updates' tag, I haven't been able to find a way to restrict 'koji list-builds' output to packages with that tag, so we're getting more than we'd like even after we use a pattern to restrict this to just Fedora 41.

(I think you may need to use the source package name, not a binary package one; if so, you can get it with 'rpm -qi rust' or whatever and looking at the 'Source RPM' line and name.)

Once you've found the package version you want, the easiest and fastest way to get it is through the koji command line client, following the directions in Installing Kernel from Koji with appropriate changes:

mkdir /tmp/scr
cd /tmp/scr
koji download-build --arch=x86_64 --arch=noarch rust-1.83.0-1.fc41

This will get you a bunch of RPMs, and then you can do 'dnf downgrade /tmp/scr/*.rpm' to have dnf do the right thing (only downgrading things you actually have installed).

One reason you might want to use Koji is that this gets you a local copy of the old package in case you want to go back and forth between it and the latest version for testing. If you use the dnf updates-archive approach, you'll be re-downloading the old version at every cycle. Of course at that point you can also use Koji to get a local copy of the latest update too, or 'dnf download ...', although Koji has the advantage that it gets all the related packages regardless of their names (so for Rust you get the 'cargo', 'clippy', and 'rustfmt' packages too).

(In theory you can work through the Fedora Bodhi website, but in practice it seems to be extremely overloaded at the moment and very slow. I suspect that the bot scraper plague is one contributing factor.)

PS: If you're using updates-archive and you just want to download the old packages, I think what you want is 'dnf download --enablerepo=updates-archive ...'.