The linux-lowlatency 6.8 kernels in Noble 24.04 will continue to exist as a separate kernel build. Although the 6.8 kernels already had the changes that allowed it to be configured for a lowlatency system we decided to not make any packaging changes to 24.04. The deprecation of the linux-lowlatency kernel as a separate build has been done only in 25.04 (see Release Notes). Therefore, if you stay with the GA 6.8 linux-lowlatency kernel and don’t switch to the HWE kernel (linux-lowlatency-hwe-24.04) you shouldn’t need to change anything in your system.
Even though the linux-generic and linux-lowlatency kernels have the same ABI numbers, they are separate packages which can be promoted to noble-updates at different times, that’s why you see the lowlatency kernel lagging behind at this moment but it should catch up over the next couple of days. Regarding apt trying to replace -lowlatency with -generic, that shouldn’t happen as we haven’t done any package change that should cause it. Could you please open a bug report and provide us logs or apt output for us to look into it?
Regarding the order that grub will pick the default kernel for you, I suspect it’s ordering the kernels by ABI so that’s why you would see -generic coming first at this time. Usually users don’t have the -generic and -lowlatency kernels installed at the same time, if you still want to keep the -generic kernel installed as a fallback but always boot the -lowlatency by default I would recommend looking into the grub configs available for setting the default kernel priority.