Alpine install USB crashes iMac 8,1 bootloader

I'm trying to install Alpine on a 2008 model iMac 8,1. However, the boot selection screen crashes if the Alpine USB is plugged in, which means I can't boot the installer.

It's not a fundamental Linux issue, as I was able to boot and install MX Linux.

I've also had the same problem on a 2010 MacBook. However, I can boot the USB on a 2014 MacBook Pro 11,2.

How can I troubleshoot this boot issue? Is there a trick to make a custom install USB which will boot on an old Mac?