Woooooowww I didn't believed anymore that this would be solvable...
Thank you Nick and Marvin for all the help.

Nick I did a little different before you posted. Instead of the UUID=something I wrote this in sh-4.2#
mount -t xfs /dev/nvme0n1p3 /
mount -t xfs /dev/nvme0n1p2 /boot
mount -t vfat /dev/nvme0n1p1 /boot/efi

(if I didn't write down the filesystem (vfat or xfs) it gave me an error)

And then did grub2-mkconfig -o /boot/efi/EFI/clearos/grub.cfg
And exit.
And it booted...

Is it OK now? Or is the buggy grub still on my system? Must I do something? Erase it or something? I don't want to fear every time I reboot the PC and pray that it would boot...

OMG... almost 1 full day of messing around with this... I was messing around with FTP for more than a week, and then this...
Just one more question... HOW CAN I DISABLE GRUB UPDATE? I don't want to do this in a month or so again, when someone decides to release such a bug again...

Thanks one more time.