After the release of iOS 14.7.1 there are several reports that device shows 'No service' message when it definitely should have service.
Apple published special provisioning profile to help with connectivity issues.
5G devices running iOS 15 and iPadOS 15 can automatically prioritize connecting via 5G instead of WiFi when the performance of WiFi networks you visit occasionally is slow, or when you are connected to captive or insecure WiFi networks. Install the 5G Preferred Over Wi-Fi profile ("profile") on devices running iOS 15 and iPadOS 15 Beta 4 or greater to greatly increase the likelihood of seeing 5G preferred over Wi-Fi connections and to ensure your networking path logic is optimized for situations where 5G will be preferred. For more information, see https://developer.apple.com/5g/.Apple Developer
According to Business Wire CCC Digital Key 3.0 standard includes support for Ultra Wideband radio. This makes Car Key even better on iPhones with U1 chip.