unknown variable 'log_slow_verbosity=query_plan'

Question

What is the use of log_slow_verbosity = query_plan parameter in my.cnf ?

I got an error when installing MySQL in my machine because of this parameter.

Answer 1

log_slow_verbosity is for MariaDB, not MySQL

Perhaps your OS has MariaDB repos installed instead of MySQL. If you downloaded MySQL and installed it, mysqld encountered an already existing my.cnf that was for MariaDB.