Based on your description, I understand that you want to delete a large amount of data in the DiscoveryHolds folder.
Based on the steps you've already taken, you can also try the following suggestions:
1.Use the Search-Mailbox cmdlet:
You can use this cmdlet to search for and delete items in the DiscoveryHolds folder. Compared to the Remove-ComplianceSearchAction cmdlet, this method allows you to delete more items at once.
Make sure that you've correctly applied and updated any retention policies that might affect retention and deletion. Double-check that Single Recovery is turned off and that the retention period is correctly set to 0 days.
You can refer to similar questions Discovery Hold - Microsoft Q&A
More information can be found Delete items in the Recoverable Items folder | Microsoft Learn
2.Manually delete messages from recoverable items
3.Automated scripts for bulk deletion
Since search/compliance search can only delete 10 items at a time, you can save time by writing custom PowerShell scripts to automate multiple deletion cycles.
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