First time. MacOS installed to HDD but won't boot.

Currently using Ubuntu on a hard drive and wanted to dual boot MacOS on it. So I followed the Multiboot Guide and created a partition for MacOS to be installed for later.

I followed the internet guide here and created a bootable usb and installed High Sierra to the newly partitioned HDD.

After the install it restarted so I went back into boot order menu and Mac OS X now appeared, however it doesn't boot from this and instead goes to the next bootable drive which is Ubuntu.

I feel like I'm missing a step, I've looked over the vanilla/internet guide but can't find any answers on what to do next.

submitted by /u/TeaRebel
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