Is there any place I can download the last version of 60.x of Thunderbird? I can not stand version 68 as it is. Too many of my extensions that I use are now useless and the last straw was this attachment issue.

Not sure what you mean by Classic Reader or Viewer (Adobe?), but you can download the TB 60 installer for Windows in the language of your choice:

https://archive.mozilla.org/pub/thunderbird/releases/60.9.0/win32/

"Classic Reader" is accessible when one clicks on the 3 vertical dots in in the upper right corner of a message body pane and select "View in Classic Reader" . That is the only way in version 68 that one can see what files you had attached to a sent email. This lack of information from the normal viewing window is astounding. Do people never have to check or open attachments for sent email?

Thanks for the archive link. In TB60 some of these extensions were still broken but at least the attachments on sent email were able to be opened and viewed by clicking on the link provided at the very bottom of the message body pane.

'View in Classic Reader' is not something I've seen in any version of TB, so it must be provided by an add-on. Attachments in sent or received mail are displayed in the Attachment Pane, below the message body. Click on the bar with the Save button to toggle the AP on or off, or right-click and check 'Initially Show Attachment Pane'.

That is the whole problem I no longer see the Attachment Pane below the message body in 68.x as I did in 60.x.

When you say "Click on the bar with the Save button to toggle the AP on or off, or right-click and check 'Initially Show Attachment Pane'."

What "Save" button?

I see no right mouse clicks giving me a 'Initially Show Attachment Pane' option.

Remember I DO see attachments for incoming mail just NOT for sent mail.

You might have a broken layout that shows up when you run TB 68. Run in safe mode (hold Shift when you launch TB) and see if the Attachment Pane and Save button appear. If it looks right in safe mode, restart again in safe mode, click 'Reset toolbars & controls' and click 'Make changes and restart'.

Found out that it is being caused by an extension called Thunderbird Conversations which seems to have an issue with TB 68 but not with TB 60.

Note that there is a version for TB 60, 2.14.7, and one for TB 68, 2.15.9.

https://addons.thunderbird.net/en-US/thunderbird/addon/gmail-conversation-view/versions/

Yup I have 2.15.9 installed here and that is where the Classic Reader appears to be from. For some reason the extension has issues with sent mail attachments and the Attachment Panel when you use the plugin's recommended settings.