I too was experiencing a repeatable crash in X3 Reunion during the first mission on Linux (mostly up-to-date Arch). I have the version from GOG. On a whim I decided to try replacing the bundled libraries in the lib/ and game/lib/ directories with packaged ones. Surprisingly that fixed the crash and I was able to finish that and eventually dock at a station so I could save after the mission.
I had to build ffmpeg 0.9.4 and GLEW 1.9.0 but all the rest are packaged. Fortunately I know ffmpeg and think it is easy and GLEW just needed a minor change to the lib32-glew PKGBUILD to build the old version. I renamed the two existing directories to lib.old and copied my newly built libavcodec.so.53 libavformat.so.53 libavutil.so.51 libGLEW.so.1.9 libswscale.so.2 into a new game/lib directory.
Now I can fly in space.
[EDIT] I spoke too soon. I now get a crash when loading that game.
X³: Reunion - Linux support thread
Moderators: timon37, Moderators for English X Forum
Re: X³: Reunion - Linux support thread
...and everyone, who crashes during first mission!
rename or delete:
X3 Reunion/lib/
libstdc++.so.6.0.19
libstdc++.so.6
libxcb.so.1.1.0
libxcb.so.1
libXrandr.so.2.2.0
libXrandr.so.2
X3 Reunion/game/lib/
libopenal.so.1
libz.so.1
system libs wll be used, crashes will disappear
mint 20.1 64bit