You need to install VLC and its media decoders. They're used for playing the cutscenes' video files. You should be able to run these as root:
Ubuntu/Debian: apt-get install vlc
RHEL/Fedora: dnf install vlc
Arch: pacman -S vlc
and it should install correctly. Remember to use sudo if you aren't a root user. If you are using the itch desktop app and installed it through flatpak, it may be sandboxed and installing VLC won't work.