Only a handful of lines at the start will be actual script, the rest is binary data. head -n 20 is probably all you'd want to use. Even so you won't be able to modify it.

The fact some of the packages installed (that were missing) is encouraging, but still concerning. Unfortunately unless there's another package we need to try getting. I hesitate to suggest installing or dual-booting an 18.04 version of linux, and we aren't sure if they will support another version of Ubuntu. And asking for support may take months...

The next logical step may be to have someone install their game, and since it probably won't need superuser access it will just install to ~/GoG Games, then tar, share and try and see if it attempts to run or not. And worst case it doesn't.

I'm sure libcrypto and libssl are both used for decrypting and installing, not for the game itself.

A deb installer is just a compressed archive, which tools like archive manager can handle (hopefully: right click, open with archive manager). Extract the data.tar.xz file, and then from that the .so files you need. Put those in the lib dir of the game to make the game use them, and that should make it all work.

On the commandline, you can extract the files from .deb installers like so:
ar x libjson-glib-1.0-0_1.4.2-3ubuntu0.18.04.1_amd64.deb data.tar.xz
(afaik it's always data.tar.xz - if that can't be found use `ar t` to list the contents.)
Then to extract everything from there:
tar -xf data.tar.xz
The .so files for libjson-glib-1.0-0_1.4.2-3ubuntu0.18.04.1_amd64.deb are libjson-glib-1.0.so.0.400.2 and the libjson-glib-1.0.so.0 symlink which points to it, from usr/lib/x86_64-linux-gnu/