Ok,I think that I have now checked the contents of /boot/initrd.img-6.10.6-amd64 and conformed that it has a correct etc/modprobe.d/snd-hda.conf entry.
And I know that modprobe operates correctly manually on snd-hda.conf. So I can't see how that initramfs can be a problem, although it is the obvious candidate since it sets up the kernel initially. It was last built on Aug 31 probably as triggered by a dpkg upgrade. It could be that I didn't notice that sound was astray until a day or so later. So I guess there has to be something astray there, but what? Or could there be another explanation? Puzzled.
