kernel updates not appearing (until grub repair tool used)

[DukeComposed]

could it be that my grub choice during the initial mx install (windows dual boot option for mx19) determined what i should have used for grub options when installing mx23

Dual-booting usually becomes a problem for reasons just like the one you've experienced. In general if you're going to pick a system to install and manage a GRUB bootloader, you should stick with that system to maintain the bootloader after any change you make. A lot of people think that if one distro uses GRUB, and another distro also uses GRUB, then they can mix and match whatever config they're using at the time and GRUB will just know what they want their disk layout to be. If you're going to dual-boot two different Linux installs, pick one to own the bootloader and keep it current.

[a2z]

thx for helping me narrow it down to this.

but the issue is that i did not know what option to select during the mx23 install to allow some 'preferred' bootloader.
as long as mx23 was functional, the whole point was to eventually migrate away from mx19, which was not going to get new kernels anyway.

and now that booting into mx19 is needed to update grub with new kernels for mx23, does this mean no fix?

[fehlix]

thx for helping me narrow it down to this.

but the issue is that i did not know what option to select during the mx23 install to allow some 'preferred' bootloader.
as long as mx23 was functional, the whole point was to eventually migrate away from mx19, which was not going to get new kernels anyway.

and now that booting into mx19 is needed to update grub with new kernels for mx23, does this mean no fix?

Maybe you missed the point, with UEFI boot you can have multiple efi-loader, which than load the GRUB loader.
(Check UEFI-Manager)
So as already suggested, stick with one efi-loader->grub-loader combo as the first (primary) to be loaded from the efi-loader order list.
In adddtion in case the other OS does also have some kernel upgrades, maybe create a custom-cfg entry to "chainload" the other grub-menu,
Otherwise you need to boot into the other OS, and refresh the GRUB menu in order the current OS can pick up the newly added kernel
from the other GRUB menu.
Still something unclear. If yes, give details description of your setup,
including partition layout : what is installed where and efi-loader list.