The keyword SLAVE was removed in mysqld 8.4 (now latest LTS), after being deprecated since 8.2 (?).
https://dev.mysql.com/doc/refman/8.4/en/mysql-nutshell.html#mysql-nutshell-removals

We use this keyword in the code at least in once place, and in documentation several places to instruct on replicating.

The replacement keyword is REPLICA, which is available only from 8.0 (2018).

We can probably require "mysql 8.0 or later" at this time.