There are no previews in the Photos app either. I can confirm however that the images are ok after import into Lightroom. I would just like to be able to do the initial screening of photos before importing all of them.
Now almost 1 year after the latest comment, it is still not showing up for me on my iPad with iOS 15.1 (Lossless compressed RAF (Fujifilm X-T4)). But on the other hand it shows everything correctly on my Mac with Lightroom (CC) before import. My question is if it wouldn't be possible to use the same logic to show the thumbnails before import used for the Mac app on the iPad? And to come back to the support of the OS itself, macOS is eighter not able to show the previews of the RAF Lossless compressed files in Finder. So Adobe did something to show them on the Mac but didn't use this logic on the iPad.
I hope it would be possible to add this to a future release, since I love the option to import the images on the go into my iPad.
In the Direct Import view, Lightroom relies on iOS to be able to display thumbnail images. If iOS can't do that, then Lightroom also cannot display thumbnail images in that view. For such images, Lightroom can only display thumbnail images after import when our app as able to process each image and make its own thumbnail images.