One idea per screen. Built for phones, Shorts and a side panel.
Why portrait
Portrait
720 × 1280. The rail moves to the bottom and the type re-fits to the narrower column.
Mixed
A single slide can override the deck default with orientation=landscape.
The test
If it needs two ideas, it is two slides. Portrait is unforgiving that way.
Use portrait for a phone handout, a Shorts clip or a side panel. Keep dense tables for landscape.
Close
Build it from Markdown, open it on any device, print it at its native size.