As there have been many changes over many years, perhaps you would be good enough to offer your definition of "the old format". It is probably possible to make a change that will suit you, but my library of changes basically start here https://kb.mozillazine.org/Make_Thunderbird_3.1_look_like_Thunderbird_2

That is my first experience of folk making statements like yours "thunderbird new style sucks". That was what, 15 years ago. So you will have to be somewhat precise in asking what you want changed because there have been a lot of changes since then. Some good and some not so much, but changes none the less.

It used to be that the list of emails waiting to be read consisted of one line with the subject, sender and time. Now the list takes up at least the equal of 4 lines for each email. I want it back to the compacted list.

Easily done. just to the right of 'quick filter' above the message list is a tiny icon. cllck that and select 'table view'

I must admit I also loath the cards view. It takes a load of space and still does not deliver what users have been asking for for more than 10 years, a couple of line preview of the content of the email like outlook does/did.

Image below as a guide