https://www.freebsd.org/projects/acpi/ seems to contain mostly outdated information or information that is no longer relevant. Maybe it needs to go altogether.
A commit references this bug: Author: carlavilla Date: Sun Dec 22 14:27:14 UTC 2019 New revision: 53706 URL: https://svnweb.freebsd.org/changeset/doc/53706 Log: Remove the ACPI information from the website. Moved to https://wiki.freebsd.org/ACPI PR: 216754 Submitted by: avg@ Patch by: carlavilla@ Approved by: bcr@ Differential Revision: https://reviews.freebsd.org/D22903 Changes: head/en_US.ISO8859-1/htdocs/projects/Makefile head/en_US.ISO8859-1/htdocs/projects/acpi/
Fixed. Moved to https://wiki.freebsd.org/ACPI