Managing OpenWrt on my AX6S router?

So I've finally managed to flash OpenWrt on my AX6S router using this tutorial:

The first thing I've tried to do was update to the latest snapshot firmware using the sysupgrade file from the OpenWrt website but that didn't end up working and I had to unbrick my router and flash OpenWrt again. Is it only accepting the firmware from that Github page?

I've also noticed that I can't select 160MHz on my WiFi 6 antenna for some reason? Well I can but then the WiFi stops working and I have to go back to 80Mhz.

Also while I'm getting 700Mbps upload now, I'm only getting 350Mbps download. That is with Gigabit fiber and Wifi 6 enabled devices. Is that normal? I did enable hardware offloading.

Tagging: @mikeeq