Both screenshots show the same change, one for a large device, one for a small device. In each one the image on the left is the current UI, the image on the right is the new UI, with changes highlighted). The changes are:
1. Move the "#", "@", and "Language" buttons in the toolbar from the right to the left.
2. Move and shrink the avatar of the account you're using to the start of the "Posting as..." text.
3. Move the "Toot" button to the top right.