So you have not mention that you system is a iMac. There you need to do extra steps because of the UEFI as i know… but i have never used a Mac, so can just research it.
Here is a little guide what could help:
https://wiki.archlinux.org/index.php/IMac_Aluminum
This might be the same issue:
I’ve got some weird booting issues. I’m on an iMac 12,2, and for some reason, under Manjaro, I have two boot options in my Mac’s boot menu (not counting the hard disk with MacOS on it, which I never boot into). The options in the boot menu (hold down alt a.k.a. Option while booting) are:
Macintosh HD (old 500GB hard disk)
EFI Boot
Recovery 10.13.6 (a recovery partition on the 500GB disk)
EFI Boot
I’ve got Linux on a 1TB SSD which I installed internally on the iMac
The first EFI Boot partitio…