You mean wider than it is tall? That's pretty much the standard format at least in biology -- it's weird when they want the other way. For example, the ASM (American Society for Microbiology) wants things 8ft (long) by 4ft (high)

https://asm.org/ASM/media/Events-PDF-s-2/Poster-Presenter-Ch...

Frankly, I've never seen a portrait format poster :)

I've mostly seen posters in portrait, just not the academic kind of poster.

In the UK all movie posters are "widescreen", which I prefer compared to the US format:

https://www.originalfilmart.com/collections/british-quad-mov...

In Machine Learning / Computer Vision I've only seen landscape posters.