https://wccftech.com/ios-15-ipados-15-prioritize-5g-over-wifi/

Both iPhone 12 and the M1 iPad Pro are the first Apple devices to feature a 5G modem, so in addition to connecting to Wi-Fi networks, users can experience blazing-fast connectivity speeds using the baseband, but again, that will depend on the connection. With iOS 15 and iPadOS 15, users will be able to prioritize 5G connections over Wi-Fi ones, but there is a condition that needs to be met.

According to Apple, 9to5Mac reports that as more apps and system experiences are enhanced by faster 5G connectivity, it will give users the ability to prioritize 5G connections, just as long as the connection is better than Wi-Fi. Improved 5G support also includes the ability to back up to iCloud and restore from an iCloud backup, coupled with streaming audio and video on native Apple and third-party apps.