Hello there,
being lazy I always have SCID installed / updated with synaptics, which means that I'm currently running 4.7.4 under Debian (Mint), which runs perfectly well including sound! I lately tried the latest 5.1x-versions, both as flatpak and directly downloaded from here. Both do not play sound and claim "snack not found at startup" - which is in fact installed and worked well with previous versions (and still works after switching back to V4.7.4). So this seems to be a bug in V5.1x.