IOS 14 (iPhone12) USB tethering
This is a known issue within ipheth that has plagued a couple of projects ever since the iPhone 12 was released. The solution appears to be reducing the MTU value from 1516 to 1514 in the ipheth.c source file, but this breaks ipheth for other iOS devices that are not the iPhone 12. More than this, editing driver source files and isn't something that "anyone" is going to do.
From what has been seen in the field so far:
- WiFi tethering with an iPhone 12 running any version of iOS 14 is broken
- USB tethering with an iPhone 12 running any version of iOS 14 is broken
- Bluetooth tethering with an iPhone 12 generally works ... so long as you don't mind Bluetooth transmission speeds. Note:
— Bluetooth 5.0 is 2Mbps
— Bluetooth 4.2 is 1Mbps
Ubuntu 21.04 should see this update included in ipheth, and it will likely be back-ported to 20.04 LTS as well. There is little chance of seeing it in 16.04 LTS as that release is nearing EOL.
While this is not a great answer, I hope it gives you something to work with.