Also being an engineer, I get annoyed when others pull the "engineer" card like it makes them magical and entitled - I've worked with a many engineers in multiple industries, and there is a wide variety of competency. I've worked with many craftspeople and others without degrees that I would trust before fellow engineers.
I know successful troubleshooting is easier when you have more data to analyze. I also realize that some amount of guessing and hypothesizing is required when you give minimal data and are asking people to solve a problem remotely. I don't have your car in front of me, and you provided limited data, so I can't see what you have or haven't tried.
Despite all of that, I have the same UI as you ("white needle"). I plugged an aux cable in this morning and and here's what happened:
I clicked "more" per the manual
View attachment 18434
That screen then showed my two USB drives as well as "aux", per the manual.
View attachment 18435
I clicked on "aux", and it was connected and working, per the manual.
View attachment 18436
Apologies in advance for guessing and hypothesizing against your wishes, but:
1. Did you restart the car and try again? There is a bug where the car occasionally doesn't recognize the USB drives if the car is started or put into gear too quickly. The same bug may impact the aux input, since it is the same module in the center console
2. Does the same aux cable successfully work on a different car or device?
3. When plugged in to USB, did the MP3 player detect that it was plugged in and appear to at least be charging?
4. Does the USB cable work in a different car or for transferring files from a computer? Some cables are charge only and cannot transfer data.
5. Have you tried any other USB devices in the center consile at any other point in time to see if the ports work? It's possible you have a bad connection from the USB/aux module in console. If you have nav and the SD card works, that likely isn't the issue.
Again, I'm just hypothesizing, but my guess is #1, since you didn't have the aux or USB icons, and it is a relatively common issue. When that happens to me, I don't have the USB icons. I don't use the aux input, so I can't confirm how it behaves in that situation.