I just tried the latest 118.0b4. The lag on the mouse-over effect as well as the high CPU usage is still reproducible for me. First I thought the new "cards view" is better, but that's just because fewer messages are visible in the message pane at a given time. As has been pointed out before, reducing the TB window size to show fewer messages also reduces the effect in the classic table view.
I just tried the latest 118.0b4. The lag on the mouse-over effect as well as the high CPU usage is still reproducible for me. First I thought the new "cards view" is better, but that's just because fewer messages are visible in the message pane at a given time. As has been pointed out before, reducing the TB window size to show fewer messages also reduces the effect in the classic table view.