Try this:

https://www.codetwo.com/admins-blog/export-exchange-mailbox-data-to-pst-with-powershell-video-guide/

~@~

New-MailboxExportRequest will only work on on premise exchange. O365 using MSOL connected doesn't have any cmdlets to perform action.

I was looking more towards O365 online tenant.

Did you also look at the link for o365, which talks about leveraging ediscovery for PST export?

Here's that link:
https://www.codetwo.com/blog/export-office-365-mailboxes-pst-ediscovery/

~@~

Yes, but I need to pull over 1k exports at once varying different sizes.