Hi Ann Monroe,
What is the extension of the attachment? Is the issue related to only one type of attachment files? And Does the problem occur only in this conversation?
To rule out the problem of Outlook desktop application, I suggest you sign into Outlook on the web and check if you can see the attachments. (https://outlook.office365.com)
We suggest you disable firewall and anti-virus program temporarily and have the sender forward the email, check if you can see that attachment.
We can also run Outlook in Safe Mode to determine if it is 3rd-party add-ins related: Press Win + R and type “outlook.exe /safe” in the blank box, then press Enter. Then have the sender forward the email, check if the attachment can be seen.
We appreciate your time and cooperation, welcome back to us if there are any updates.
Thanks,
Linda