Comment 2 for bug 1856392

"I have no internal mic detected.", that is because the internal mic connects to PCH instead of codec, so it needs the sof driver to enable the internal mic. Please have a try with latest mainline kernel, and upload the dmesg, the dmesg will tell us if your machine need sof driver or not.
https://kernel.ubuntu.com/~kernel-ppa/mainline/v5.5-rc1/

"When hooking a microphone enabled headphone on the jack plug, the headphones mic is then detected, but there is now no sound output on the headphone.", that should not happen. when you plug a headset, the headphone should be the output device, and the mic on the headset should be in the input device.