I have some more data points:- 1) I regenerated initrd.img-6.10.6-amd64 using # update-initramfs -uv and rebooted. The problem remains.
2) I reverted to kernel 6.10.4-amd64 ( with its rw-r--r-- 1 root root 14M Aug 24 12:14 initrd.img-6.10.4-amd64) and all was well. Comment: I have only just noticed the large difference in the size of initrd.img-6.10.4-amd64 (14M) and of initrd.img-6.10.6-amd64 (8.1M) I assume, but have not checked, that they use the same compression, if any. Maybe this is a kernel regression of some sort after all? Does this bug need to be re-assigned? Maybe there is some kernal debug parameter that might help with diagnosis?