I’m assisting a student that needs to use Blynk in a science fair where there will not be reliable WiFi. She needs to build a simple UI on the iPhone and this will control servos on the device a couple of feet away. Ideally I wanted to use Bluetooth as it seems ideal for this but it’s not clear if it’s supported, it doesn’t appear as an option in the Quick Start. As a last resort I’m willing to add either a local WiFi router or a laptop. My other question: does Blynk have to have a connection to the cloud?
No, it’s not supported in Blynk IoT.
Yes, all communication goes via the Blynk cloud servers, so you’ll have no functionality without an internet connection.
You can try FreeRTOS. No matter whether there is an internet connection or not, FreeRTOS code will keep running.