I have exactly the same problem. In my case, the output voltage to the case LED is 2.3 V, which seems to be not enough to make it turn on.
I’ve seen other posts on the forum with this problem, for example: https://forum.gl-inet.com/t/gl-atxpc-may-have-a-design-issue/64693/5.
Motherboard: GIGABYTE Z790 Gaming X AX G10
PC Case: Fractal Design Define 7
ATX Board: KVM-ATV-V1.0
I’ve sent an email to GL.iNET support. I don’t understand how this issue, which apparently has been known for months, still doesn’t have a solution.