I have the same problem with QuickBooks Enterprise 2023 Desktop.  The problem started in late June.  Now, when we email any of the following: Quotes, Sales Orders, Purchase Orders or Invoices the attachments that are connected don't appear as an attached file in the email opened by QuickBooks.  In every case all the connected attachments are visible before we choose to email and the attachments can be opened using the "Attach File" icon on Quote screen which is the same with other documents I listed above that we send.  We used the Tool Hub with QuickBooks support and we ran the feature to reattach all the files.  No option provided by support has resolved the issue.  The suggestion from ChristineJoieR so far have not fixed the issue and they seem to be far from the issue.

Furthermore, we have 10 users where each uses a fast Windows 10 Pro PC and all were able to email the documents with the attached files a month ago.  I expect our Controller for our company installed an update an I will be starting with a fresh install soon, with no updates, and opening our company file on a PC local  to drive see if Intuit sent an update that broke this feature, or if Microsoft with their latest version of Outlook is the root of the problem.

ANYONE ELSE?  Does anyone at QuickBooks know if this BUG was introduced through an update?  Or do you have another option to fix this issue?