Right now only the latest entry in the changelog is displayed to the user when they run the update command.
It would be nice to show them ALL of the changes that they are upgrading through!

The text that is seen by the user after an update is currently returned in this update method
https://gitlab.wikimedia.org/repos/releng/cli/-/blob/3440a732b28fc53b96ad754628c360374ef030aa/internal/updater/gitlab.go#L70

This is the release.Description of the version being updated to.

In order to provide more release notes this method will need to retrieve the descriptions of all releases between the current release, and the release being updated to.

This will need different / more calls to the gitlab API as part of the update process.

Contribution guide...

The code repository is on the Wikimedia gitlab instance https://gitlab.wikimedia.org/repos/releng/cli and is written in GO
Documentation for mwcli is at https://www.mediawiki.org/wiki/Cli (This includes an installation guide, and first setup guide for the dev environment).
If you want to pick up this task please ask @Addshore to be added to the project first. This way you will be able to create a branch on the repository and have CI run.