Very cool. Is there no way around the need for a boot disk? A boot disk implies also bringing the USB-C to USB adapter everywhere, and it's a bit cumbersome.
Yes, I was able to get Grub setup on my internal drive, so now I just boot directly into PureOS and hold down option to boot to macOS. I'll def have that info in my next entry, but you basically just copy the Grub config files I link to in the post to your internal drive's EFI partition (without deleting the Apple stuff that's there).