Hi and welcome to the forum 
Please see:
It is not clear where you installed your Manjaro, because you say different things:
So please post info as instructed in that page i linked above so people wanting to help you have more relevant info on your hardware.
Extra info which might be needed are the outputs of these commands:
- efibootmgr -v
- sudo lsblk -l
- and perhaps sudo fdisk -l to check for partition type codes.