Just updated (2022-5-7) and on reload the message view list was 50% larger per item than it was before. It should be relatively simple IMHO (as a Software Developer [largely web-based] of 20+years) as I have had to include such a feature within a release package more times than I’ve eaten Ready Salted crips.
What I meant to say was that it should be relatively simple to keep the Look and Feel chosen by a user across upgrades (unless a feature has been removed of course). In this particular case, it wasn’t the spacing defined for the list (as I haven’t changed that) but rather that after the upgrade the list included “No preview available” for the contents of the emails in the list. This prompted a Help search which gave a solution that was for a previous version - hence the other topic.
The preview lines in the message list is a new feature in version 9. If the first 1-3 lines of the message don’t have text that is previewable, then we display that no preview is available.