Sorting mail in Thunderbird by both unread status and by date
Solution 1:
Click the settings button while looking at your inbox (the 3 hatch marks upper right on your inbox view) point to "view" then "sort by" choose "read". If necessary go in again and choose sort order "Descending" It will sort unread to the top, by date, and then read by date, both descending.
Solution 2:
Go to the settings box in the upper right of Thunderbird, go to view then sort by, make sure date is selected then in the below column select descending. Then the settings will save after closing. I'm not positive I understood the question but this is what I believe you want.