/usr/lib/libplplotqtd.so.1 is in plplot12-driver-qt 5.10.0-0ubuntu5.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/libplplotqtd.so.1.0.0
/usr/lib/libplplotqtd.so.1.0.0