Starting with Bookworm /boot/cmdline.txt was maoved to /boot/firmware/cmdline.txt. Therefore rpi-clone can unfortunately no longer update the UUID of the clone and the clone no longer starts. Details are described here on github.
Unfortunately, rpi-clone is no longer maintained. A solution was worked out in the github issue which I have implemented in my clone of rp-clone. This means that if you get rpi-clone from my git repository, you can use rpi-clone to create a bootable clone under Bookworm.
Jeff Geerling has agreed to take over the maintenance for rpi-clone in the future. His rpi-clone fork can be found here. All previous fixes have been consolidated in this fork and rpi-clone now creates bootable clones on Bookworm again.
If you missed to upgrade to the fixed rpi-clone version 2.0.23 and created an unbootable clone don't despair. With my small script syncUUIDs you can very quickly correct the wrong UUIDs and then the faulty clone boots again.