Extend M365 Archive Quota capacity

Yes, since you are on the Office 365 E5 license, your users are eligible for auto-expanding archive mailboxes. By default, archive storage starts at 100GB, but Microsoft automatically increases it in 100GB increments up to 1.5TB and beyond as needed, based on usage.

Once a user's archive mailbox reaches 90% of its capacity, Exchange Online starts expanding it in the background. There's no need for manual intervention, but it can take some time depending on the load.

You can check if auto-expanding archive is enabled using PowerShell: 

Get-Mailbox "User Name" | FL ArchiveStatus,AutoExpandingArchiveEnabled 

And to enable it (if needed):

Enable-Mailbox "User Name" -AutoExpandingArchive

If you hae reached the upper limits and it's not expanding, I’d recommend raising a support ticket with Microsoft for further review.