Thanks for reaching out. We are sorry for the trouble with Adobe Lightroom on mobile.
Could you please share one of the sample images where the tools did not function? Have you tried with images where the sky or the subject is prominent and is not blurred out?
Please click on this link (https://lightroom.app.link/5Pdyw272qpb) to begin a tutorial from the Learn tab on Adobe Lightroom mobile app, you can continue to edit the image and test the Select Sky tool on this image. Similarly, you can use another tutorial image (with people, animals, and foreground objects) to test the Select Subject feature on Lightroom Mobile and share the results here.