Actually no :/ The problem is that sensors produce images in 3:4 aspect ratio. The only way to show a full screen preview is to apply a crop, but then, when you take a photo, will either get

• an image that is different from the preview,
• or get a cropped image. What the system camera app does to give the illusion of being full screen is to blend a frame from the main camera with a frame from the ultrawide, but this approach isn’t allowed with manual exposure/focus.

If I get requests about this specific feature I can consider implementing, but will probably deliver cropped images.