Xiaomi recently started rolling out MIUI 184.108.40.206.OEIMIFA update for the users who updated their devices to MIUI 220.127.116.11 update that was deleted soon after release. The latest Android 8.1 Oreo-based MIUI stable update comes with the version number MIUI 18.104.22.168.OEIMIFA, and the changelog mentions Android Nougat to Android Oreo upgrade for India, optimised dual 4G function and other fixes.
Redmi Note 5 Pro users who have not received a notification, can go to Settings > About phone > System update > Check for updates. As mentioned, since this is an OTA update, it might take a while before it lands on your smartphone. But, you also have the option to download it or get the actual ROM files directly. The Recovery ROM can be installed used the Updater app, however, the Fastboot ROM will require an unlocked bootloader.