I have a problem similar to the one described here: 20.04: internal speaker (Audio) is not working in Ubuntu 20.04 LTS after upgrading from Ubuntu 18.04 LTS
None of the solutions posted there worked for me, also the problem is a bit different in my case.
In a summary: since I've upgraded to Ubuntu 20.04, the audio normally works for me. However, sometimes after I put my system in standby and then resume it, my audio no longer works and I see only "Dummy output" in the list of audio output devices.
Restarting the computer solves the issue for me. However, it's quite annoying that I have to restart it every time.
sudo lshw -C multimedia *-multimedia description: Audio device product: GP104 High Definition Audio Controller vendor: NVIDIA Corporation physical id: 0.1 bus info: pci@0000:01:00.1 version: a1 width: 32 bits clock: 33MHz capabilities: pm msi pciexpress bus_master cap_list configuration: driver=snd_hda_intel latency=0 resources: irq:17 memory:f7080000-f7083fff *-usb:0 description: Video product: USB 2.0 Camera vendor: Sonix Technology Co., Ltd. physical id: 1 bus info: usb@3:3.1 version: 0.00 capabilities: usb-2.00 configuration: driver=snd-usb-audio maxpower=500mA speed=480Mbit/s *-multimedia description: Audio device product: 8 Series/C220 Series Chipset High Definition Audio Controller vendor: Intel Corporation physical id: 1b bus info: pci@0000:00:1b.0 version: 04 width: 64 bits clock: 33MHz capabilities: pm msi pciexpress bus_master cap_list configuration: driver=snd_hda_intel latency=0 resources: irq:32 memory:f7330000-f7333fff