no audio on fresh install kubuntu groovy

[Bob H]

on installing Kubuntu Groovy 'no output or input devices found'
sound appears to be disabled
running ubuntu-debug -s audio does produce sound in both headphone channels in first part of test but no sound in second part
sound is recognised and working okay if Kubuntu Focal is installed

ProblemType: Bug
DistroRelease: Ubuntu 20.10
Package: alsa-base 1.0.25+dfsg-0ubuntu5
ProcVersionSignature: Ubuntu 5.8.0-34.37-generic 5.8.18
Uname: Linux 5.8.0-34-generic x86_64
NonfreeKernelModules: nvidia_modeset nvidia
ApportVersion: 2.20.11-0ubuntu50.3
Architecture: amd64
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/controlC0: bob 1071 F.... pulseaudio
                      bob 1074 F.... pipewire-media-
 /dev/snd/controlC1: bob 1074 F.... pipewire-media-
 /dev/snd/seq: bob 1070 F.... pipewire
CasperMD5CheckResult: skip
CurrentDesktop: KDE
Date: Thu Jan 7 03:19:48 2021
PackageArchitecture: all
SourcePackage: alsa-driver
Symptom: audio
Symptom_AlsaPlaybackTest: ALSA playback test through plughw:SB successful
Symptom_Card: Built-in Audio - HDA ATI SB
Symptom_Jack: SPDIF Out, Internal
Symptom_PulsePlaybackTest: PulseAudio playback test failed
Symptom_Type: None of the above
Title: [MBB-895908, Realtek ALC892, SPDIF Out, Internal] Playback problem
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 04/07/2014
dmi.bios.release: 4.6
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: 2501
dmi.board.asset.tag: To be filled by O.E.M.
dmi.board.name: M5A99FX PRO R2.0
dmi.board.vendor: ASUSTeK COMPUTER INC.
dmi.board.version: Rev 1.xx
dmi.chassis.asset.tag: 7354844-001
dmi.chassis.type: 3
dmi.chassis.vendor: NOVATECH LTD
dmi.chassis.version: 1.0
dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvr2501:bd04/07/2014:br4.6:svnNOVATECHLTD:pnMBB-895908:pvr1.0:rvnASUSTeKCOMPUTERINC.:rnM5A99FXPROR2.0:rvrRev1.xx:cvnNOVATECHLTD:ct3:cvr1.0:
dmi.product.family: To be filled by O.E.M.
dmi.product.name: MBB-895908
dmi.product.sku: SKU
dmi.product.version: 1.0
dmi.sys.vendor: NOVATECH LTD

[Bob H (bobbicat)]

*addition*
when running Kubuntu Groovy from a thumbdrive usb iso, audio appears to be functioning okay.

[Bob H (bobbicat)]

When I submitted this report I wasn't aware that this issue had been mentioned in the Release Notes (which weren't available at the time)
...that means this report is not required.