The OEM driver for the audio will need to be removed then reboot then reinstall the OEM driver. Otherwise its using the Generic HD audio driver and will not DETECT anything plugged in. View full driver details [URL] This procedure will need to be done with EVERY windows feature update because the realtek security files are often hijacked by malware Microsofts response to this is to delete ALL the drivers but its in such a way that the OEM driver is broken in the process every time. Bluetooth, audio, wifi and other Realtek drivers are stomped on again and again by microsoft.  
Neither the rear mic input nor the rear line in seem to be recognised. In the Sound Control Panel (Windows 10) Recording tab, it says "Not plugged in" on both, even when they are.   The Properties Jack Information for both says "Front Panel jack" - which explains the "not plugged in" (nothing is plugged into the front panel jack), but is obviously not true otherwise.   Both are set to "enable". As I understand it, the front panel jack - with headpone icon - is a "combo jack" designed for headphone and mic combined.  I presume that's why it doesn't register either a stereo or mono mic plugged into it.  (I don't have the 3-ring plug necessary to check if it would work that way.) I do sometimes use the front panel jack for headphones (and it works), but normally I used speakers plugged into the audio out (which is working fine).  Incidentally, the Speakers / Headphones device in Playback says Rear Panel Jack, even when headphones are plugged in the front. I have of course checked that the devices I plug into the mic or line in sockets (as appropriate) are working otherwise. Recently I have been using a USB audio interface for sound input, which the system does recognise as an additional "microphone", and it works, except I find I can't quite get the volume levels I want (even with levels set to max in the sound control panel), which is why I want to try my equipment with either the mic or line in. (I do realise line level signals should not go into the mic!)  
Read audio inputs not working on Inspiron 3268