re :in POP3 was able to keep mail in INBOX on the server or servers and when I deleted mail on my device is was always just the local device inbox that move the mail to local device trash.

Correct. Pop accounts can only access the server to download a copy into the Pop Inbox. You have the option to download and delete off server or leave a copy on the server. Although you do need to keep an eye on webmail account as any emails deemed as Spam by server will be moved to server Spam folder and you will not even know this occurred. Pop accounts also tend to have a smaller quota space on server, so it is worth while checking every now and again to delete very old stuff off the server. Pop accounts do not synchronise folders so what you see in a Pop account can be very different from what is on the server.

Imap accounts are very different. Imap accounts can only show what is on the server in any folder that has been subscribed to be seen. Imap account folders synchronise with server folders of same name to show what is held on the server. Basically the imap folders are one and the same as the server folders. You delete an email from an imap folder and it will get deleted off server. You delete an email whilst accessing the webmail account and when you look in Thunderbird it will also get deleted. This means you can access that email address from various computers eg: at work, at home or via a phone, if all are accessing via imap or accessing webmail then you will see an identical copy of what is on the server.

You should not consider imap account folders as a separate copy because the folders synchronise.

re: What is the configuration solution in IMAP land to just pull off the server what is "new" and only delete the local copy out of the local device inbox?

You cannot. You do not have a 'local' copy if it is in an imap folder. It is not independent of server. You have to work around it by using the system.

If both of you are accessing same email address to see emails, then create suitable folders and move emails into them. You could create a folder with your name eg: 'Bob' Only you subscribe to see the 'Bob' folder You Move only your emails from 'Inbox' into 'Bob'

Your spouse could also create a folder called eg: 'Jo' Only the spouse subscribes to see 'Jo' folder Spouse Moves only the emails for spouse from 'Inbox' into 'Jo'

This means whilst the server still has a copy of everything, Bob is not seeing Jo's emails (and vis versa) because you have not subscribed to see the 'Jo' folder. You leave new unread emails for both of you in 'Inbox' and create some folders for organising which both of you subscribe to see eg: 'Family', 'Friends'

So use the facility of creating and subscribeing to see your own sets of folders, so do not need to see a load of stuff you do not wan to see.

If there are certain emails from a particular email address eg: 'info@xxx.com' that will only ever go to you, then you could create a Message Filter. eg: If 'from' 'contains' and type 'xxx.com' then move message to Bob folder on imap account. This will help auto sort emails.

Hope this info helps you to understand how imap functions and how you can get it to work better for you.

The only other option is to use the 'Local Folders' mail account. Make sure your setting really are downloading full copies and not just headers see info: https://support.mozilla.org/en-US/kb/imap-synchronization#w_configuring-synchronization-and-disk-space-usage

and then copy only your email into the 'Local Folders' mail account folder. Create folders in 'Local Folders' mail account to organise your emails. This will allow you to keep a local copy in Thunderbird that is independent of the server. You then can choose whether to delete email from imap account folder and thus off the server, whilst retaining your own copy.

Basically, you would be leaving emails that both need to see in the imap folders. Each of you would be moving own personal emails off server into respective 'Local Folder' mail account folders.

The 'Local Folders' mail account will be different on each computer. Completely separate folders independent of server.

The previous method I suggested is where you created and subscribed to see own folders within the imap account itself. Then each would only see what they had subscribed to see.