sql_safe_updates in my.cnf not work

Hio,

set global sql_safe_updates=1;

set local sql_safe_updates=1;

works properly, but adding
sql_safe_updates=1 tigger this error

"unknown variable 'sql_safe_updates=1'"

Already reported years ago for MySQL 5.5 here:

https://bugs.mysql.com/bug.php?id=66536