The license header in wintab.h says:

The text and information contained in this file may be freely used,
copied, or distributed without compensation or licensing restrictions.

This license does not explicitly allow for modification and for making derived works. This makes it incompatible with DFSG.

qt_attribution.json says that this file is public domain, which is not true.

Moreover, the website says that they are not distributing the software anymore due to a patent lawsuit settlement.

This is not a big problem for us in Debian, as we will just strip that directory from the tarballs, but I am filing this bug to make you aware of these issues.