Many things stop working on kernel update
I am currently running Debian 12 with Gnome using the 6.6.9-amd64 kernel, and have had quite the issues with the newer kernels. Once i switch to them in the grub menu, I am only able to use a single monitor which has been set to a sub-normal resolution. Also animations for the DE are all gone. I can't add my other monitors in, my nvidia settings panel lost most of its settings (from about 20 tabs to 3) and the entire system runs really poorly. While part of this seems to be an nvidia thing, I do wonder how I would actually go about fixing this.
Sounds like your NVIDIA driver isn't loading for the newer kernels. Either not compiled for them, or not installed, if Debian ships it in binary form. The easiest solution would be to not install newer kernels. It seems you're already ahead of the default Debian 12 kernel - 6.1.
DKMS isn't installed or is broken. The whole point of it is to update things when a new kernel gets installed.
Yeah, unfortunately that's not always possible as modules don't always build against newer kernels. Also I don't know if Debian uses dkms for this. On Ubuntu for example, NVIDIA modules are shipped in a pre-compiled form for the supported kernels instead of using dkms.
Would it maybe make sense to install this older 6.1 kernel? It would potentionally have greater compatebility with the driver... Also, this probably does not have anything to do with the kernel thing, but I just reid to apt upgrade, and found this message repeated a bunch of times at the end of it:
This seems like an error which should not be shown to the user and instead the developer of apt, which apparently uses cp.
Yeah, it's not an error.
Yes I would stick with the default kernel unless I have a good reason to change it. E.g. there's functionality I really need.
You want to run a stable debian kernel, not "bleeding edge" stuff from the backports repo. It's likely that your NVIDIA drivers are not compatible with the more modern kernel, either for real reasons (they're old) or because that's how they were packaged.