If no Nest devices show up in HomeKit after set-up, the most common cause is that you have signed into the wrong Nest or Google Account when setting up your hub. You need to sign into the same Nest or Google Account that you use to sign into the Nest app (and/or Google Home app) on iOS.
You can check that you have signed into the correct Nest or Google Account by going to the Starling Home Hub app, Troubleshooting and Support and checking Nest Devices Available. If this list is missing Nest devices that you own, or shows speakers but no other kinds of devices, it means you are signed into the wrong account. Find out which account you are actually using in the Nest or Google Home app, and then go back to the Starling Home Hub app and sign into that account.
If you're certain you've signed into the correct account
Occasionally, a glitch can occur when adding HomeKit devices via the Apple Home app which leads to incomplete set-up.
Please return to the Starling Home Hub app, then factory reset your hub by going to Troubleshooting and Support, then Factory Reset. Then, follow the on-screen instructions to complete set-up again and re-add to HomeKit.
If you still have issues, then please contact Starling Support.