Ubuntu 22.04 kernel 5.15.0 boots to zero screen brightness on Lenovo P51

I have a Lenovo P51 upgraded to Ubuntu 22.04 LTS;It now boots to a black screen (subtle behavior, read on).The graphics hardware available are Intel Corporation HD Graphics P630 and NVIDIA Corporation GM206GLM, and the kernels available are 5.15.0-43-generic and 5.15.0-43-generic.

Behavior:

• Kernel 5.15.0-43-generic: Briefly boots to an empty desktop with cursor before halting at a solid black screen (not a desktop session with zero screen brightness).
• Kernel 5.15.0-41-generic: Boots briefly to a normal tty1 login prompt, then to a gray screen with a visible mouse cursor, then to a fully working normal desktop with the backlight brightness at 0. I can dimly see that expected windows are present and system is responsive. Keyboard brightness controls do nothing.
• Kernel 5.15.0-41-generic (recovery mode): Boots normally—but there is no keyboard or software control of screen brightness.

If relevant, I'm booting into a mate-session (Ubuntu Mate).

This behavior emerged yesterday after a reboot following apt-get upgrade; Prior to this, the system had been running continuously for 2–3 weeks and seemed OK with the exception of these warning signs:

• I lost keyboard control of screen brightness.
• In the months prior, the system would never resume after closing the laptop lid (jet black screen, not the working screen with brightness zero described for 5.15.0-41 above).

As you might imagine, I've spent the usual day's labor combing through other forum posts and following debug steps for vaguely similar issues, but haven't been able to solve it. Any ideas?