The Tall Man

That's already a topic (with a solution):
https://forum.armbian.com/topic/55129-trixie-apt-warning-policy-will-reject-signature-within-a-year/
 

That module is not included in the default kernel build configuration. But you can build the kernel yourself.
 
https://docs.armbian.com/Developer-Guide_Build-Preparation/
https://docs.armbian.com/Developer-Guide_Build-Commands/
 
When you run ./compile.sh, the first thing it shows you is the kernel configuration screen (image 1). Select, "Show a kernel configuration menu before compilation".
 
When it finally arrives on the configuration menu (image 2), use the forward slash key (/) for search, enter ntsync. When the result comes up (image 3), press 1 to select it. It will take you right to it. It will be highlighted (image 4). Press the M key to select it as a module. The use the right arrow to move from Select to Exit, and keep doing that until you get to where you save it. Then keep going with the rest of the process.
 
I could be wrong about this, but I think you can build the kernel only without the whole armbian image too, with this (from the second link above);
./compile.sh kernel-config BOARD=orangepi5 BRANCH=edge  
Image 1: Select Kernel Configuration

 
Image 2: Kernel Configuration Menu

 
Image 3: Search Result - NTSYNC

 
Image 4: - NTSYNC Selection