Please see https://dev1galaxy.org/viewtopic.php?id=5255 where I  posed a similar question. I will let you read that thread and judge whether your situation is the same.   

Wireguard works well with both the .armmp kernel and the kernel optimised for RPi.

I concluded it was better to stick with the optimised kernel but it may be horses for courses!

Installing the wireguard package requires another kernel - 6.1.0-14-rt-armmp.
I installed it and removed the current 6.1.64 kernel. However

uname -r

stil returns 6.1.64.

After some research I found that the actual booted kernel is the one in

/boot/broadcom/kernel7.img

. I believe that apt doesn't generate this specific img file (it generates the initramfs files though...).

I wonder how to generate the kernel7.img file without building custom kernel myself? Probably from the initrd.gz file? Or just putting vmlinuz-6.1.0-14-rt-armmp as kernel7.img ?

Otherwise I find these instructions proper for the task: https://www.raspberrypi.com/documentati … ernel.html