WN3000RPv3 not seeing 5 GHz band on BGW320-500 gateway

My WN3000RPv3 extender does not seem to see the 5 GHz band on the AT&T Humax BGW320-500 gateway. I have 8 other devices that do connect on 5 GHz.

If I connect my iPad using the gateway, I get 398/357 Mbps to the gateway and 359/346 to my device, which is great.

BUT, if I go through the extender to my iPad, I get 398/357 Mbps to the gateway and 19/17 to my device. I had expected a 50% drop to about 200 Mbps, but 19/17 is ridiculous.

So, I have 2 questions:

1. Would I see an improvement if the extender used the 5 GHz band?

2. How do I get the extender to see the 5GHz band and use it?

Running Win 10 22H2 on Lenovo A530 desktop using ASUS AC35 USB adapter