I entered the commands by looking at the page here https://pve.proxmox.com/wiki/Recover_From_Grub_Failureyou appear to have done a bind mount on /dev and /run, but not on /boot so there is not /boot.
Are you following a guide in your steps? If not - you should pick one.
Blockbridge : Ultra low latency all-NVME shared storage for Proxmox - https://www.blockbridge.com/proxmox
sudo vgscan
sudo vgchange -ay
sudo mkdir /media/RESCUE
sudo mount /dev/pve/root /media/RESCUE/
sudo mount /dev/nvme0n1p2 /media/RESCUE/boot
sudo mount -t proc proc /media/RESCUE/proc
sudo mount -t sysfs sys /media/RESCUE/sys
sudo mount -o bind /dev /media/RESCUE/dev
sudo mount -o bind /run /media/RESCUE/run
Are you sure you are using grub?
See conversation here: https://forum.proxmox.com/threads/grub-not-updating-with-update-grub.68699/#post-307970
Blockbridge : Ultra low latency all-NVME shared storage for Proxmox - https://www.blockbridge.com/proxmox

grub-install /dev/nvme0n1 and it will use the less than 1MB between the partition table and the partitions, as usual.We use essential cookies to make this site work, and optional cookies to enhance your experience.