Hi, I just installed Kubuntu 18.04 and I have no audio.
I have two monitors (with built-in speakers), one connected by Display Port and the other by HDMI.

If I connect headphones, for example, I do have audio, but if I disconnect them, the audio does not come out either through the standard audio output (green jack to the monitor) or through HDMI.

I've downloaded the PulseAudio and Alsa mixer, and spent time fiddling with the options, but there's no way.
I already ruled out that it was a problem with the integrated speakers of the monitors, since in Windows it works perfectly.

I ask for help to solve this problem.

Thanks in advance.

Any reason why you didn't install Kubuntu 20.04 if you want an LTS version? Makes little sense to install a version that will reach its EOL this spring...