In TB, you have the email profiles at the top in the lh pane and the offline folders in a separate place below them. You can make folders here and then click-drag the files into them to make a local copy.

I don't see a Local Folders entry in the left-hand pane; not sure if that matters.

It does. Did you rename the Local Folders account at some point, or did you attempt to delete it?

Also, please post your Troubleshooting Information. At the top right of the Thunderbird window, click the menu button , then select Help > Troubleshooting Information. Press the "Copy text to clipboard button" and paste the information into your reply.

> Did you rename the Local Folders account at some point, or did you attempt to delete it?

Not that I recall; certainly not recently (last few years). I did shift from POP to IMAP years ago. I see under "Account Settings" a heading for Local Folders, at the same level as my two IMAP accounts.

Rather than post the 34K troubleshooting info inline, I uploaded it to TB troubleshooting info but I can post the whole thing here if needed.

As per your Troubleshooting Information the 'Local Folders' account exists.

What do you see in your folder pane? Please post a screenshot with all accounts visible. https://support.mozilla.org/kb/how-do-i-create-screenshot-my-problem