This is most definitely not suitable for mobile. The default Lemmy UI is optimized for mobile.

Similarly, this is what I see with Alexandrite on my ultrawide using a tiling window manager. Whereas Lemmy fits perfectly. And I really like how Lemmy’s responsive UI shows the community sidebar when there’s enough width to do so, which will often contain very useful info for members browsing posts on the community.

So no, I don’t think this UI has been optimized for anything other than a maximized window on a FHD display.

The layout doesn’t work very well with narrow window widths, or on mobile screens. It’s only comfortable to use if you expand the window to at least a 1080p window width, so it’s not very useful on a desktop using tiling window management.