When in "Layout > Vertical View" mode, and switching the Thunderbird window from one (small) screen to another (big) screen, the ratio between the "Inbox pane" and the "Message pane" is not preserved.
The current behavior seems to be that the width (in pixels) of the "Message pane" is preserved.
Which means making the "Inbox pane" increase dramatically when moving from a smaller screen to a bigger screen, effectively leaving a big unused space.
I think the behavior in Thunderbird < 115 was to keep the ratio between both panes.
Another behavior that could fit is to preserve the width in pixel of the "Inbox pane" rather than the width of the "Message pane". It would be more relevant because user choose the "Inbox pane" width so it fits all needed columns on screen.