Microphone not working using headset (ubuntu 20.04)

Hello all,

I'm using optiplex 7070 mff, running ubuntu 20.04 (out of the box, never reformatted)

I wish to abandon my laptop for this, but I'm a teacher, and  covid-19 determines I have to be able to video conference.

The pc setup has to audio ports on the front - Line Out & Headphones.
I'm using "gamers" headset, which connects through single trrs 3.5 jack. I also bought a spliter (1F -> 2M).

No combination of connection seem to detect me using the mic.

Thanks in advance,

Gal

P.S. I do not believe the problem lies with the Linux OS, for the laptop runs the same one, and the headset works well out of the box.