Support For AMD Renoir with a new driver was only available from June 2020 with v5.8 kernel
Linux 5.8 Sound Changes Bring New AMD Renoir ACP Driver - phoronix.com
This has the new driver snd_rn_pci_acp3x which appears to be the AMD equivalent of sof-firmware drivers for Intel laptops, supporting buit-in digital microphone array DMIC
Intel laptops needed the latest development version (13.99) of Pulseaudio to get recent patches for audio support
and Intel SoundOpenFirmware was released before AMD Audio Co-Processor
This from Arch forum confirms that latest version of Pulseaudio is needed for AMD
[SOLVED] Microphone not working on Thinkpad T14s / Multimedia and Games / Arch Linux Forums
so I recommend installing pulseaudio-git from AUR
Another Manjaro user posted recently that they had to remove packages
libao, fluidsynth, lib32-fluidsynth and manjaro-pulse to get pulseaudio-git installed
and then reinstall the packages again
HP Envy - Sound does not work in Manjaro 20.1 PLASMA
(I have also just noticed that manjaro-pulse is only a metapackage so installing it again is not really necessary)
I don’t want to draw to many parallels with Intel hardware, but pulseaudio 13.99 got a 4 speaker (and 4 microphone) Intel laptop working
Lenovo ThinkPad X1 Carbon (Gen 7) - ArchWiki
It might do the same for this hardware 
but it should at least get you closer to a full working solution