Hello @hafizuddin shahipurullah
Please visit https://support.microsoft.com/en-us/topic/-the-remote-server-returned-an-error-404-or-http-request-has-exceeded-the-allotted-timeout-error-when-you-move-a-mailbox-from-on-premises-exchange-server-to-exchange-online-04f3586e-d52e-5fbb-093a-03dc9a34cd8d for more information than provided below.
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Please don't forget to mark as correct answer if this helps.