Your partition layout is EFI.
The EFI partition size indicates a former Windows system.
Switch the system firmware to use EFI.
Boot a live USB - then follow [root tip] [recovery] Basic Manjaro Linux Rescue and Recovery
EFI is a boot loader it self - which need firmware entries to identify which loaders are present and where they are stored.
GRUB is yet another boot loader which - is a part of the Manjaro ISO.
The lack of boot entries in the firmware - the following is a guess - may have been caused by a firmware update where your boot entries has been removed or by a failing CMOS battery.