I believe no distro actually ships this version of awk by default. They ship GNU awk which has Unicode support anyways.
$ awk -V
awk version 20211208
Kernighan's version is likely used in other places where the GPL is eschewed. $ awk -version
awk version 20200816 # awk -version
awk version 20210215 $ echo 'ö' | awk '{print length}'