I appears that they may now have a BIOS for the GK3 that includes Secure Boot.
https://www.iacepc.com/forum/viewtopic.php?p=5389#p5389
From the above linked post...
admin wrote: ↑Wed Oct 27, 2021 6:35 am I am very happy to share this news with you. We have developed a safe start function for GK series machines. If your GK series models are restricted by safe boot and cannot be updated to Win11. You can contact me through the after-sales mailbox: 18898767762@163.com, I will send you a new version of the BIOS for you to use. When contacting, you need to attach a photo of your BIOS main interface so that I can confirm your BIOS version.