[Book Catalogue 7.0.4-distplay on Pixel 7 running Android 16 BP4A.251205.006]
Adding a thumbnail (either to existing book, or to a just-added book) via Cover Options > Replace Thumbnail ... - I take the photo then go to the screen where I adjust the crop and the Cancel/Save buttons are both greyed out (and unfortunately, are also under the Android navigation buttons - which doesn't actually show up on the screenshot). Couldn't figure out a way to proceed, even after moving the crop rectangle around a bit.

[Book Catalogue 7.0.4-distplay on Pixel 7 running Android 16 BP4A.251205.006]
Adding a thumbnail (either to existing book, or to a just-added book) via
Cover Options > Replace Thumbnail ...- I take the photo then go to the screen where I adjust the crop and theCancel/Savebuttons are both greyed out (and unfortunately, are also under the Android navigation buttons - which doesn't actually show up on the screenshot). Couldn't figure out a way to proceed, even after moving the crop rectangle around a bit.