I have already read this discussion here:
https://forum.manjaro.org/t/grub-is-shim-lock-enabled-not-found/159220
but the guy who looked for help, was able to boot into one of the two efi-boot-options and then could reinstall Grub with pacman.
The other source, I already had discovered is:
The user cites some code, how to proceed for reinstalling Grub. But it is not clear, that this would really work. He shares this proposal:
# mount the btrfs root subvolume
mount /dev/sda1 /mnt -o subvol=/
# (optional) set the default subvolume
btrfs sub set @ /mnt
mount /proc /mnt/proc --bind
mount /dev /mnt/dev --bind
mount /sys /mnt/sys --bind
chroot /mnt
grub-install /dev/sda
update-grub /dev/sda
# activate first partition
fdisk -l /dev/sda
And they refer to a wiki article which should be found here:
https://wiki.manjaro.org/index.php/GRUB/Restore_the_GRUB_Bootloader
but actually this website is down.
I also had found this source here:
https://bbs.archlinux.org/viewtopic.php?pid=2157953#p2157953
Someone describes a solution which could work for me also, but my knowledge is too limited and I cannot go the single steps, he has done.
At the end, there are too many questions unanswered, so that I am scared to try something which would perhaps ruin my system finally.
Oh I would like to mention:
- disabled TPM
- disabled CPM
- disabled secure boot
- List item