OpenWrt Based Modem + OpenWrt Router Help

First of all, I am very new to this whole networking thing so I may or may not understand the solutions given but I'll try my best to understand. So basically I have a 5G modem with its custom firmware based on OpenWrt (it doesn't have as much freedom, more like a plug and play config) and I'm trying to use the OpenWrt router like a dumb access point so I can turn off the wifi from the 5G modem and use the router's wifi instead to reduce the load, the thing is I can't config SQM and adblock with it as it doesn't have internet connection.

Here's what I've tried :

  1. Config the router as dumb access point
  2. Same as above? I didn't delete wan interface on this so it has internet access

On #1 above, I get full speed 400-500mbps exactly like when I'm on the modem's wifi

On #2 above, I can config SQM and adblock but it ignores it and my internet speed drops significantly to 70mbps-140mbps.

Any best solution to this?

if you can't customize the modem settings, you need to NAT the connection between the modem and the openwrt device.

check the CPU load of your openwrt device while SQMing, it required some CPU, install and run htop via ssh.