Whoops!!
Sorry but I missed you post that you added since my last visit here.
I will l;eave the rest of this however just in case it helps in any other situations.
Firstly, I hope I have understood exactly what you want on your computer, which is that 24.10 should be the default OS that you boot into from grub and that you want 24.10 to be the OS that manages grub rather than either of your older versions.
Try booting into 24.10 from whichever grub you currently have and from 24.10 use command
Code:
sudo grub-install --target=x86_64-efi --efi-directory=/boot/efi --bootloader-id=ubuntu --recheck --no-floppy
This has worked for me at least twice, maybe more times, and the system now manages and uses grub from the OS that I want, ie, the OS from which I ran that command, in my case 24.04 as I use LTS versions only.
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