The Librem laptops (L13 and L15) currently sadly do not support external microphones, at least if you are looking for a 3.5mm jack mic. You can though of course attach something that has USB, which I would recommend for quality reasons anyway - there are USB headsets for example.
The new Librem Mini does support mic input on the 3.5mm headphone jack.
Thanks for link @kieran , I will come back to solving this issue during the one week break at the end of this semester (4 weeks left). I will also give a procedure update, at that time, in my original thread regarding my VM use situation & Yeti USB Microphone.