Debian packages for CGAL 6.0 are now available as well. Simply add

  deb http://debian.cgal.org bullseye main
  deb-src http://debian.cgal.org bullseye main

  deb http://debian.cgal.org bookworm main
  deb-src http://debian.cgal.org bookworm main

to /etc/apt/sources.list (you only need the pair of lines
corresponding to the release you are using) and make sure that the
package apt-transport-https is installed. For sid/unstable,
packages are available from the official Debian repository. The
packages are called libcgal-dev, libcgal-qt6-dev, libcgal-demo,
and libcgal-ipelets.

In case you want to download the packages manually, have a look at
https://debian.cgal.org/pool/main/c/cgal/ .

See also https://www.cgal.org/FAQ.html#debian_packages .