I tried installing BG:EE and it failed.

Running Baldur's Gate Enhanced Edition
./BaldursGate: error while loading shared libraries: libjson.so.0: wrong ELF class: ELFCLASS64

I'm no Linux expert, but BG:EE is not 64 bit. Doesn't that 'ELFCLASS64' suggest the libraries are of the wrong architecture?

Yeah that is exactly right. I had to install all the required libraries in 32bit. Why is GOG assuming the installer will install 32bit versions of the libraries if that is what it needs?

GOG packages what the the developers provide. If Beamdog haven't made it clear to GOG that 32 bit libraries are needed, then that's Beamdog's fault.

I see so we have Beamdog to thank. That makes sense since their own client uses an appimage and Ubuntu isn't even setup to use app images for their recommended system specs and they don't wrap it in a bash script to perform even a rudimentary check and install for the user. The steam install works out of the box though so clearly they care more about the steam builds or since the steam client requires i386 to run maybe that trickles out to the other libraries required and it accidentally has overlap?

I also just noticed the required packages are listed perfectly on the store page, but didn't make it into the installer as such.

libc6:i386 libasound2:i386 libasound2-data:i386 libasound2-plugins:i386 libjson-c2:i386 libopenal1:i386 libstdc++6:i386 libssl1.0.0:i386 libexpat1:i386 libx11-6:i386 libxau6:i386 libxcb1:i386 libxcursor1:i386 libxdmcp6:i386 libxext6:i386 libxfixes3:i386 libxinerama1:i386 libxrandr2:i386 libxrender1:i386 libjson0:i386

They did not include the 32bit packages in the installer because of some compatibility issue. If I remember correctly, a blue (staff member) explained that was the better way to go to stay on the safe side.

I believe you already solved your problem.