You might have noticed that your iPhone and iPad now save photos as HEIC (HEIF) files rather than JPEGs. Blurb's design tools do not support HEIC/HEIF files.
If you're using BookWright or BookSmart, your photos must be in either the JPG/JPEG or PNG format. This means you'll need to convert HEIC images to one of these formats before placing them in your book.
To convert your HEIC files to JPG/JPEG images, check out Apple's instructions under the Converting this media section. (You'll need to first open the HEIC image on your Apple laptop or desktop computer in order to convert them).
Apple also provides instructions on how to change your device settings so your iPhone or iPad will save photos as JPEGs. Review the second part of the Capturing this media section.
Blurb can't help you convert your HEIC images or change your iPhone/iPad settings but the links above will take you directly to Apple's instructions. You can also search Apple's help center for HEIC.