Let me repeat once again (from my initial post): try chrooting and reinstall the grub. 
The BIOS Fast Boot disabled is also not really by chance: it solved a very similar issue a few months ago.
By-the-way, in your rescue steps, shouldn't it be (hd1,gpt4) or (hd0,gpt4) according to your specs above? You should point to /dev/nvme0n1p4, your root partition, not the EFI partition.
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