Nothing is cropped any more
Players used to fill the screen by cutting off whatever did not fit. A 4:3 slideshow on a widescreen TV lost the top and bottom of every slide, including titles. The whole slide is now shown at its own shape, with black bars filling the rest. A slideshow that already matches its screen looks exactly as before.
A proper 4:3 option
Older PowerPoint decks and many PDFs are 4:3. They were treated as square and squashed to three quarters of their width. There is now a Landscape 4:3 resolution, detected automatically and available in every resolution picker.
Thumbnails for every kind of slideshow
The Slideshows and Devices pages show the first slide as the cover, whatever type it is. A slideshow made only of live or media slides no longer shows a blank grey box.
A clearer schedule on the device page
A device with several schedule entries shows the previous, current and next slideshow side by side, with the current one marked ON AIR. A device with one slideshow assigned directly shows it in a card instead of "No schedule set".
What this means for you: what you see on the dashboard is what your audience sees, whatever shape the screen is.