First, I'm still using
Mojave macOS 10.14, so I don't really have any experience in
Catalina macOS 10.15How did Entourage denote attachments?
Could that 'information' have been lost in the conversion process?
I've never used the "Attachments" column.
Enabling it surprised me by displaying a message that had 4 but I had never noticed anything in the message. I'm also now sorting several mailboxes to see if there are some attachments I have missed. I must also admit that I don't remember ever seeing the paperclip icon beside a sender name, although I now see it!
I also see a series of tabs appearing when I hover the cursor over the sender
line. Among other things,
it includes a drop down list of 'attachments'. OK, you can also see this hidden interface when hovering over the thin grey line separating the header and the message regardless of the presence of any kind of attachment.
Do you also see this? Not sure it's relevant, anyway.
OK, I have found a few messages that claim to have attachments according to the column. But I have also found a couple that have that icon but
not an icon beside the sender name. The attachments are a a PDF and two PHP files and display the normal OS 'file' icon with name at the bottom of the message.
Other messages include the paper clip icon in the column and beside the sender name but display images directly in the message.
All in all, I'm not seeing any point for the column in my use: I either see the attachment at the bottom of the messages or enable viewing images for that message. Since I usually keep Safari and Mail windows open beside each other any time the iMac is running, I'd rather have more room for the message sender and subject along with the date/time received. But that's my opinion and not an answer nor help to your question.