/usr/lib/x86_64-linux-gnu/libSDL_gfx.so is in libsdl-gfx1.2-dev 2.0.25-4.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libSDL_gfx.so.15.9.1
/usr/lib/x86_64-linux-gnu/libSDL_gfx.so.15.9.1