Same bug as I reported here: Brume 2 policy routing dns leaks - #19 by teleney (might need to scroll up a little) this was on the brume 2. I believe it's addressed on my Brume 2 now but obviously might need applying to your firmware too?
My way of making the router resolve again was to stop wireguard client, go to network > DNS. Change the DNS to any other setting than it is and click apply, then change back to "automatic" click apply - if you dont see the options then make sure adguard is disabled. Once you have adjusted the settings in the DNS then re-apply adguard home (if it was enabled) turn on the Wireguard client again and now your router should resolve / update packages.
If you reboot the router and the Wireguard client is enabled then the same problem will happen, you would need to repeat the same steps.