People don't usually understand that apt allows you to configure multiple sources across versions simultaneously, so you can e.g. run stable, but also selectively install from backports or unstable.

To do so, add the sources for trixie-backports and unstable, and add the following configuration (e.g. /etc/apt/preferences.d/trixie-sid-pin) so that the system knows which sources your prefer:

   # Default to trixie
   Package: *
   Pin: release n=trixie
   Pin-Priority: 990
   
   # Very low priority for sid
   Package: *
   Pin: release n=unstable
   Pin-Priority: 100
   
   # Give backports medium priority
   Package: *
   Pin: release n=trixie-backports
   Pin-Priority: 500

Now the system can access the latest kernel from unstable (and backports), while keeping everything else on stable:

   # apt policy linux-image-amd64
   linux-image-amd64:
     Installed: 7.0.12-1
     Candidate: 7.0.12-2
     Version table:
        7.0.12-2 500
           500 http://deb.debian.org/debian unstable/main amd64 Packages
    *** 7.0.12-1 100
           100 /var/lib/dpkg/status
        7.0.10-1~bpo13+1 500
           500 http://deb.debian.org/debian trixie-backports/main amd64 Packages
        6.12.90-2 500
           500 http://security.debian.org/debian-security trixie-security/main amd64 Packages
        6.12.86-1 990
           990 http://deb.debian.org/debian trixie/main amd64 Packages

I believe the kernel in backports gets updated only after it is live in unstable for at least a week, which lately still feels like forever.