I'm using the M4 too.

I set mine to AP and using the AX20 to do the routing.

Better for performance because the unit no need to do everything except wireless connectivity only.

If u not familiar, leave it.

U need some networking skills to do what I did for my set-up.

It is always best not to let the router do everything from a firewall, AP, routing, and file server.

The same goes for mesh.

In your case, if u already have an existing router that works, just change the operation mode of M4 to AP. Ensure u also disable DHCP on the M4 if enabled by default to avoid double NAT.

Once the router works and is online, disable WiFi too. This way, u plug off 1 potential security hole.

All WiFi businesses let the M4 handle it because u can monitor it using the Deco app.