https://www.theverge.com/2017/8/29/16221562/instagram-portrait-landscape-photo-albums-carousel

Instagram now lets you post photo albums with landscape and portrait pictures. Since the feature was introduced in February, you’ve only been able to post square-format photos — very old-school Instagram. But now, you’ll be able to post pictures in the format of your choosing, rather than cropping down to a square.

The downside is that it seems like you’ll still have to choose one photo format and then stick with it — from the sound of it, you won’t be able to create an album with landscape and square or portrait photos.