MySQL Enterprise Backup User's Guide (Version 8.0.43)
mysqlbackup also backs up the .MYD files, .MYI files, and the .sdi files associated with the MyISAM tables. Files with other extensions that are backed up are shown in Table 1.1, “Types of Files in a Backup”.
            While MySQL Enterprise Backup can back up non-InnoDB data
            (like MYISAM tables), the MySQL server to be backed up must
            support InnoDB (i.e., the backup process will fail if the
            server was started up with the
            --innodb=OFF
            or
            --skip-innodb
            option), and the server must contain at least one InnoDB
            table.
          
MyISAM tables and these other types of files cannot be backed up in the same non-blocking way as InnoDB tables can be. They can be backed up using the warm backup technique: changes to these tables are prevented while they are being backed up, possibly making the database unresponsive for a time, but no shutdown is required during the backup.