How to configure audio

I run openSuse Leap 15.2 with KDE plasma 15.18.6. When the built-in speaker is used by some program, the volume, which is very low, cannot be adjusted. When I click on the speaker icon in the panel, I see a pop-up window entitled "Audio Volume" with 2 tabs: - "Devices" with the message "No output or input devices found" and - "Applications" with the message "No applications play or recording audio". Why is the built-in speaker not recognized by KDE or Leap 15.2? How can I force the system to recognize the speaker? Thanks in advance and best regards, Wolfgang