/usr/lib/x86_64-linux-gnu/libtk.a is in tk-dev 8.6.0+9.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libtk8.6.a
/usr/lib/x86_64-linux-gnu/libtk8.6.a