@karl fish: Updates are rolled out in batches, and may reach some customers sooner than others. If you head to Settings > Software update > Auto download over Wi-Fi, then you will be set up to receive the update as and when it is made available in your region.
If you have access to a home computer, then you can also try downloading the update using Smart Switch. To begin with, please follow the link below, and click on 'How Do I Get Smart Switch On My PC or Mac' to download the relevant version
https://www.samsung.com/uk/support/mobile-devices/how-do-i-backup-my-smartphone-to-my-pc-or-mac/
Once installed, open Smart Switch, connect your S20 Ultra using the USB cable that came packaged with the device, and look for an update prompt on the landing page, next to your device details. I hope this helps.
