ISC's DNSSEC Guide has been incorporated into BIND manual. Please use this new URL: https://bind9.readthedocs.io/en/latest/dnssec-guide.html
Source code of the guide can be found here: https://gitlab.isc.org/isc-projects/bind9/-/tree/main/doc/dnssec-guide
To report issues please use this new URL: https://gitlab.isc.org/isc-projects/bind9/-/issues