In order to get Starsector (not installed via the Lutris.net installer, because that uses a a very old version of the game), I had to add libXtst.so.6.1.0 and the symbolic link libXtst.so.6 to ~/.local/share/lutris/runtime/Ubuntu-18.04-x86_64/ from the Ubuntu 18.04 libxtst6 package.
In order to get Starsector (not installed via the Lutris.net installer, because that uses a a very old version of the game), I had to add
libXtst.so.6.1.0and the symbolic linklibXtst.so.6to~/.local/share/lutris/runtime/Ubuntu-18.04-x86_64/from the Ubuntu 18.04 libxtst6 package.