Linux 6.7.3 + 545.29.06/550.40.07: ERROR: modpost: GPL-incompatible module nvidia.ko uses GPL-only symbol '__rcu_read_lock'

Perfect!
I just did a apt update from Debian 12.4 to 12.5 (6.1.0-17-amd64 to 6.1.0-18-amd64) and it wouldn’t finish building the module. I tried purging and reinstalling, same thing.

Building for 6.1.0-18-amd64
Building initial module for 6.1.0-18-amd64
Error! Bad return status for module build on kernel: 6.1.0-18-amd64 (x86_64)
Consult /var/lib/dkms/nvidia-current/525.147.05/build/make.log for more information.
dpkg: error processing package nvidia-kernel-dkms (–configure):

After searching and reading numerous posts, of which really never provided a solution for me, I came across this thread and thankfully I read all the way down.

I would like to add to your post, for those that don’t have backports in their sources.list, to add the following line to their /etc/apt/sources.list file.
deb Index of /debian bookworm-backports main