Hi, @SURAJ KALAMBE
Based on your description, I understand that you want to download emails from the online archive to .pst and remove them from the online archive.
This process is divided into two main steps:
1.Export the email to a .pst file.
2.Empty the online archive.
The following article details how to export to a .pst file. Export emails, contacts, and calendar items to Outlook using a .pst file - Microsoft Support
When you empty your online archive, make sure that you have completely deleted the messages and not just moved them to the Deleted Items folder.
Others may be having the same problem as you, and the links below are available for your reference. How to export Exchange Online archive mailbox? - Microsoft Q&A
Also, I noticed that you posted the same issue, you can continue to monitor this thread. Online archive mailbox is almost full. - Microsoft Community
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