Dear BB,
Good day! Thank you for posting to Microsoft Community. We are happy to help you.
Per the description shared, I would like to summarize your requirement i.e., you would like to delete the default Attachment column in the SharePoint Online List.
If my understanding of your requirement is correct, I would like to let you know that it's not possible to delete the Atttachment column but you can disable it so that it won't show the Attachments column in the List Form.
Open the List> Settings> List Settings> Advanced Settings
After disabling it when you edit or create a new item:
Thanks for your cooperation.
Sincerely,
Mia | Microsoft Community Moderator