when I click on an email within Thuderbird program (on my PC) and chose `Save As' and choose "Text" the saved text email no longer includes the attachments

Export the message as .eml, which is plain text as well.

when I save an email this way, whether as a text file or .eml, the file is saved with date stamp and sender info in the filname. Can I turn this off?

I don't think so. However, you can try the ImportExportTools add-on and use that to export messages. https://addons.thunderbird.net/en-US/thunderbird/addon/importexporttools-ng/

Get the addon import export ng and you get more options.

Thanks for your suggestions. I save emails as .txt files if they have simple information in them that is not added to by html. This way they take less space than saving as .eml-text. To the respective suggestion, although .eml files are text files when they are saved as .eml-text they save the full bytes. Saved as .txt they are often a lot smaller.

Before some recent TBird update the saved .txt files also recorded the name and size of any attachments (not saving the attachments per se as Mime text or other text unless it was an attached .eml). I would like to go back to this and would like to ask TBird developers to simply return this simple functionality.

Adding a date stamp and sender information to the filename of a file saved to disk is also new. Who asked for this? (rhetorical question). This should be an option that can be turned off.

I'll look into the add-on you both suggested but the simple default should be a file as saved with the Subject as the filename.

Thanks, again.

the simple default should be a file as saved with the Subject as the filename.

The idea was to use unique file names when exporting multiple messages at once.