I would like to fix grub2 with kubuntu 20.04 LTS live DVD after failed neon 20.04 upgrade that left my system with
grub rescue>
which fails because insmod statements fail due ultimately to "symbol grub_file_filters_all not found"

When the neon upgrade failed at the end with a system that was unstable, I restored my prior neon 5.19 installation on the /dev/nve0n1p3 ext4 partition with Clonezilla, but grub was damaged.
So I have a GPT partition table.
With booting into a kubuntu 20.04 live DVD I opened Partition Manager which shows my disk without Win10 dual boot. Instead I have Win10 in a VM.
On the SSD's first partition is /dev/nve0n1p1 on fat32 with 37MB of which 5.98 is used.

What do you suggest?

I'm no expert on 'Buntu's coz I've been on Arch for years before Neon but the principle is the same - you'll probably need to re-install grub2 and have it update to search for your OSes. You need to look for ubuntu related info, not Neon, here's what I found on google for you to begin with:

https://howtoubuntu.org/how-to-repair-r ... tu-live-cd

Thanks, robgriff444,

That sounds reasonable and I have seen similar.
I hesitate now as I did not find a date on the Ubuntu advice or any comment about GPT partitions, etc.

Also I have not seen warnings anywhere so I will use your Ubuntu link later this morning in a couple hours as a guide unless someone provides an argument that this kind of classic linux advice is not good for GPT partitions, UEFI, etc., all the more recent new complexity.

I have to run some errands for a couple hours....

robgriff444 and all,
Following the Ubuntu link you provided, the re-install and update-grub went smoothly despite all the new complications.
I have a working system and will now look ahead to when I have time to devote to "nuke and pave" the upgraded neon.