This app does not include System Shock's game data - it's copyrighted,
proprietary content that can't be redistributed. To play, you need to
own a copy of System Shock: Enhanced Edition (e.g. from gog.com),
installed (on Windows, or via Wine/Proton on Linux).

Using SideQuest (or any MTP file browser) with your Quest connected,
copy its res/data/ and res/sound/ folders directly into:
  /sdcard/questshock/res/data/
  /sdcard/questshock/res/sound/
They already contain everything needed, in the right layout - no
merging or extraction required.

(shaders/ and this app's default soundfont are already here, extracted
automatically on first launch - only res/data/ and res/sound/ are
missing.)