MySQL 5.7, alongside other many improvements, brought bulk load for creating an index (WL#7277 to be specific), which made ADD INDEX operations much faster by disabling redo logging and making the changes directly to tablespace files. This change requires extra care for backup tools. To block DDL statements on an instance, Percona Server for MySQL [&]

https://www.percona.com/blog/2020/12/22/redesign-of-lock-ddl-per-table-in-percona-xtrabackup/