Generally, yes, but please see your mainboard BIOS manual to verify the exact procedure; it can vary per manufacturer.
Note that the quoted commands would not have completed successfuly as there was nothing to separate them.
Either enter them as separate commands;
grub-install --target=x86_64-efi --efi-directory=/boot/efi --bootloader-id=manjaro
update-grub
…or, like this:
grub-install --target=x86_64-efi --efi-directory=/boot/efi --bootloader-id=manjaro && update-grub
Notice the && between the commands.
At this point, more information would be needed to allow others to form an opinion. Please provide system information as described (below), as well as the outputs of the following commands;
lsblk -fcat /etc/fstab
I’m sure someone will help when they are able.
Regards.
Welcome to the Manjaro community
As a new or infrequent forum user, please take some time to familiarise yourself with Forum requirements, and the many ways to use the forum to your benefit:
Update Announcements
The Update Announcements contain important information and a Known Issues and Solutions section that should generally be checked before posting a request for support.
System Information
While information from *-fetch type apps might be fine for someone wishing to buy your computer, for Support purposes it’s better to ask your system directly; 
Output of the inxi command with appropriate parameters will achieve this (naturally, formatted according to forum guidelines) and will generally be more useful for those wishing to help:
inxi --filter --verbosity=8
or the short form:
inxi -zv8
- inxi man pages (Arch Manual)
Be prepared to provide output from other commands whenever asked. It’s equally important to provide as much actionable information as possible in your first post, rather than simply indicating there is a problem.