I made an initial try of Jitsi Meeting on my Lenovo T420 laptop running Kubuntu 18.04 :LTS using my Chromium browser (80.0.3987.163) an it found my built-in webcam but not my built-in mcrophone (according to the warning box). his browser was downloaded from the Google Website onto my system.
I tried it again on my Firefox browser (part of the distribution) and it seems to work OK except that I am warned that this is an UNSUPPORTED browser. (huh!)
I reooted my machine into Windows 10 and everything seems to work nicely with the chrome browser.
I then changed machines to an old desktop 32 bit machine that currently runs Windows 10 with the chrome browser and everything seems to work nicely with my Logitech Pro 9000 webcam-microphone.
Not that I have yet to hold a meeting with this jitsi meeting software.
Also, the screen shows that the webcam is operating, but I do not see an opportunity to prove that the microphone is working!
Finally note that I expect to update my Linux operating systems to Kubuntu 20.04 LTS soon after its release, but 18.04 should be supported for another year.