RPi 4, LinuxCNC upgrade doesn't upgrade kernel

Raspberry Pi 4 Model B Rev 1.2
Mesa 7c81
Debian GNU/Linux 12 (bookworm) 6.1.54-rt15 #1_RT Fri Nov 17 17:02:27 AEST 2023 aarch64

I installed LinuxCNC 2.9.3 from the linuxcnc ISO image a couple of years ago, and upgraded to 2.9.4 yesterday by:
$ sudo apt update  && sudo apt full-upgrade

I now have:
rick@raspi4:~$ dpkg -l | grep linux-image
ii  linux-image-bcm2711-rpi-4            6.1.54-rt15-1                           arm64        Linux kernel, version 6.1.54-rt15
rick@raspi4:~$ dpkg -l | grep linuxcnc
ii  linuxcnc-doc-en                      1:2.9.4                                 all          motion controller for CNC machines and robots (English documentation)
ii  linuxcnc-uspace                      1:2.9.4                                 arm64        motion controller for CNC machines and robots
ii  linuxcnc-uspace-dev                  1:2.9.4                                 arm64        PC based motion controller for real-time Linux

rick@raspi4:~$ uname -a
Linux raspi4 6.1.54-rt15 #1 SMP PREEMPT_RT Fri Nov 17 17:02:27 AEST 2023 aarch64 GNU/Linux

Is there a newer RT kernel then the one from 2023 ?
If so, how can I upgrade the kernel without having to reload the entire system from the latest ISO image ?

TIA,
Rick
 

In all honesty if the kernel gives no issues I wouldn't bother upgrading, from memory there isn't much of a difference in performance.