The BIOS worked correctly right before the installation. The tutorial tells you to switch to AHCI etc and I did this, so I can confirmed there were no problems. However I have read this issue can be related to not switching from CMS to UEFI or something like this but I do not know what this actually means?
I used the regular manjaro installer and manual partitioning as mentioned in the tutorial. I created a boot, swap, root and home partition
Here a screenshot from my grub rescue
Do I need to set the cmdpath differently since it directs to a unresolved filesystem?