Well, let's repeat booting the LiveUSB again.
sudo mount /dev/nvme0n1p1 /mnt
Since GRUB can manage Windows bootloader, let's see if we can knowck the priority for Windows off its pedestal:
sudo mv /mnt/EFI/Microsoft/Boot/bootmgfw.efi
/mnt/EFI/Microsoft/Boot/bootmgfw.efi.bak
Ensure GRUB bootloader is present:
ls /mnt/EFI/ubuntu
It it is not, repeat these steps:
sudo mkdir -p /mnt/EFI/BOOT
sudo cp /mnt/EFI/ubuntu/grubx64.efi /mnt/EFI/BOOT/BOOTX64.EFI
Once it is present:
sudo umount /mnt
Reboot and test