man mariadb-dump makes several references to an option --insert-into:

... (or INSERT IGNORE if --insert-into is specified)

... The format of the output is affected by --replace and --insert-into.

... The --insert-into option will cause CREATE IF NOT EXIST forms of SQL to generated if available.

However, this is an unknown option:

mariadb-dump: unknown option '--insert-into'

I believe it should say --insert-ignore instead.