GCP Cloudsql Mysql Replica unresponsive after mass delete on Master

Directed here from S/O We have a Master/Replica configuration for Mysql innodb(5.7.32) databases in Cloud SQL... We have a single Table (let's call it Master table) partitioned on Two keys having both primary and non-clustered indexes... It's a row-based replication with automatic disk increase on both instances... It's not a HA configuration so it's not a failover replica... *What we're trying to do...* We're trying to purge the master table back to N number of days... This is done for multiple reasons so let's say this is a client requirement... *What's the issue...* Whenever we're purging the master table it just stalls the replica, it deletes a certain number of rows on the replica and then just passes out... The number of records in a single purge is around 5 million rows... It's a totally repeatable issue... we know it's caused because it's a row-based, sequential replication so *What we've tried so far...* 1. Increasing the size of the replica, we've given it 104 GB RAM but the lag doesn't go... 2. Restarting replica 3. RESET SLAVE 4. Trying enabling parallel replication https://cloud.google.com/sql/docs/mysql/replication/manage-replicas#configuring-parallel-replication ... every single time I tried this it failed with an 'Unknown error occurred'... 5. Trying setting it to a Statement-based replication by the SET binlog_format="STATEMENT" command but the "root" user doesn't have the privilege and gets an 'access denied' error... Now the question... *what am I missing in my:* 1. explanation 2. mysql configuration 3. method Thanks