Substance 3D Designer 2022 - sbscooker can't find libGLU.so

**Game information**
Substance 3D Designer 2022

**Distribution name and version where applicable**
Gentoo/Systemd/KDE

**Flatpak info**
flatpak --version
Flatpak 1.12.3

flatpak --gl-drivers
default
host

**Problem description**
Application launches correctly but thumbnail generation and substance publishing doesn't work.

Looks like SD runs another file called sbscooker to do the work. That file fails because it can't find libGLU.so.
Below is the error generated by the application:

Error:
/home/bugg/.var/app/com.valvesoftware.Steam/.local/share/Steam/steamapps/common/Substance 3D Designer 2022/sbscooker: error while loading shared libraries: libGLU.so.1: cannot open shared object file: No such file or directory

I was able to locate the libGLU.so on my system:

/home/bugg/.var/app/com.valvesoftware.Steam/.local/share/Steam/ubuntu12_32/steam-runtime/usr/lib/i386-linux-gnu/libGLU.so.1
/home/bugg/.var/app/com.valvesoftware.Steam/.local/share/Steam/ubuntu12_32/steam-runtime/usr/lib/i386-linux-gnu/libGLU.so.1.3.08004
/home/bugg/.var/app/com.valvesoftware.Steam/.local/share/Steam/ubuntu12_32/steam-runtime/usr/lib/x86_64-linux-gnu/libGLU.so.1
/home/bugg/.var/app/com.valvesoftware.Steam/.local/share/Steam/ubuntu12_32/steam-runtime/usr/lib/x86_64-linux-gnu/libGLU.so.1.3.08004
/usr/lib64/libGLU.so
/usr/lib64/libGLU.so.1
/usr/lib64/libGLU.so.1.3.1

I'm not sure if the wiki entry about missing symbols applies in this case.

**Does this issue reproduce with native Steam**
Have not tested