JMB9: No, sorry - sound works fine here on two machines ... AMD with Ubuntu 20.10 and Intel/Nvidia withMint 19.
We just wrote to the developers about the following bugs (still) in the new 1.2.58g (46619):
1) The DLC does not exist for the latest version under Linux (current DLC just installs the old version alingside the DLC).
2) The special attack (acid pool or laser barriers) sometimes still stay after death of the causing ferocious enemy.
3) After our opinion the balance of the new Family Trials is lacking and is way to difficult in normal.
4) From time to time scrolling is jerky - with AMD Zen2 (Ryzen 5 3600) and RDNA1/Navi 10 (Radeon RX 5700 XT).
5) In Family Trials the exit portal appeared once next to a trap that kept pushing the players away.
and hope for some improvements - especially concerning the ballance of the new mode - and the missing DLC, of cause.
But we are pleased as now it is fun to play while the former 1.1.70.3 (40979) was extremely buggy under GNU/Linux.
We never experienced a sound problem - yet - with a lot of days playtime ... so maybe HW dependant - just a guess -
if you don't have sound problems with other programs ...
No, the hardware is okay, sound works for everything else.
The only thing that comes to mind is that I replaced PulseAudio with PipeWire a few months ago, maybe there's some kind of incompatibility with Children of Morta. I don't care enough to switch back to PA just to test this, though, because like I said, works fine everywhere else. Other Linux games, Wine games, Spotify, Firefox, etc. have zero sound issues.