Using TVInfo(SeriesDisplay) or TVInfo(SeasonDisplay) definitely works, thats what my views use.
Any other expressions are however problematic, since its not really clear to what their result will be.
The coverart mode is determined by the view itself, not by what a particular entry in a view might represent, as such a mixed view that shows both TV series and anything else will likely not be able to show you Series cover art, unless you somehow assign series tags to those other entries and still group by that (and only that).
Note that you can override the "Expression to Display" to your liking, just the "Expression to Group by" has to remain one of the ones mentioned above, as appropriate.
My Season expression for example adds the show name to the output as well, so it says "Show - Season 1" (well with a new line instead of a dash), and season covers still work since thats only the display expression.
You can only set up views like that in Theater View, not Standard View.
There's no option to group by an expression and then display using another in a Standard View list.
You can set up a
category like that, but it doesn't seem to work there either, and that doesn't help with grouping the list of episodes.
I set up two views showing the problem.
1. Upper pane categorized by [Season], lower pane grouped by [Season]
2. Upper pane categorized by an expression grouping with [Season] and displaying TVInfo(SeasonDisplay), lower pane grouped by TVInfo(SeasonDisplay)
For my views, I don't want multiple categories being used.
With a single category, double-clicking a series brings up a list of all the episodes.
With multiple categories double-clicking a series drills down into additional views (like the ones pictured) which I don't like.
That's good for Theater View navigation with a remote, but a list is better for Standard View navigation with a mouse.