/usr/lib/x86_64-linux-gnu/libSPlot.so is in libroot-math-splot-dev 5.34.14-1build1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/root5.34/libSPlot.so
/usr/lib/x86_64-linux-gnu/root5.34/libSPlot.so