External mic not working anymore on Macbook Air

I have a Macbook Air "Early 2014" with OS 10.11.6.

A few months ago, I used a lavalier mic plugged into the headphone/mic jack of this Macbook Air. I recorded lots of audio narrations of presentations that way. My lavalier mic uses the 3-striped TRRS type of male plug.

(In case it's relevant: over the past few months, I've updated the OS whenever prompted to, and I've also played with audio extensions such as Soundflower to allow recording of Skype calls.)

Now, my Macbook seems unable to use my lavalier mic. And it also fails to record audio from my iPhone headphones (which also use a 3-striped TRRS type of male plug and have a built-in mic).

I've tried to completely uninstall Soundflower and any other audio related programs / extensions.

I know that my lavalier and iPhones headphones mic still work because I've tested them with other devices today.

So there seems to be a problem either with the Macbook Air port (extremely unlikely) or with some sort of software or setting (very likely).

Without completely reformatting my drive and reinstalling OS X, how can I figure out why my mic no longer works and fix it?

P.S. When I do try to record, the tiny embedded microphone built into the left of the keyboard is what is recording (instead of my plugged-in mic). I know this based on my tapping on the external mic and tapping on the keyboard to determine the loudness of which sounds get picked up. Thanks.

P.P.S. I've already read these posts, and they are not helpful for my situation because I already know about TRRS and what kind of external mic to use and have one that has already worked:

• External Microphone input for MacBook Air 2012
• MacBook Pro (mid-2012) Microphone Input
• https://superuser.com/questions/361980/recording-with-audio-input-macbook-air

I had the exact same problem on my MBP late 2015 (running Catalina 10.15.7) with a Rode Mic and a TRRS adapter. Everything was perfectly fine and during a live transmission the mic went dead. I had to quickly switch to my AirPods (awful sound compared to a external mic) to complete the transmission.

I tried ALL possible solutions documented on the web and Apple Support pages. MBP would just not recognize it anymore on the Sound properties.

I tried SMC reset, NVRAM reset, upgrade to last patch (I was one patch behind), upgrade to Big Ser (new OS).. nothing.

I decided to reinstall and restore from Time Machine, since I didn't have interest in running Bigsur yet. Voilà!!! Worked!

It seems the reinstall + Time Machine restore fixed something that was corrupted in the OS.