RBR20 to AP mode as extra satellite

You will not be happy to read this...... Sorry.

An Orbi router is the base of a WiFi system, whether in router or access point mode.  It can never be a satellite attached to another Orbi router.  When this RBR20 is placed in access point mode and the WAN (yellow) ethernet port is connected to one of the LAN ports of the router, this RBR20 will ask for (and receive) an IP address from the primary router.  This IP address will appear in the primary Orbi Attached Devices web page.  It will behave just as any other access point from any vendor would behave.  i.e. it will manage devices that are connected to it and will not coordinate anything with the primary router.  A device begins a dialog with it and says, "I want to connect", and it will connect.  The device will ask for an IP address and the access point will say, "I am just an access point, I don't do that", and send the request up to the primary router.

This RBR20 may have exactly the same WiFi name (SSID) and password as the primary Orbi, but they are different systems. (Just as a random access point from Best Buy would be a different system.)  The primary difficulty will be that devices do not roam seamlessly between the two WiFi systems.  If everything connected to this RBR20 never moves, then this will not be a huge problem.  But, smart phone, tablets, and laptops move around a lot.  "Why is my laptop so slow all of a sudden?  Oh, I moved from the area covered by the primary Orbi to the area covered by the RBR20.  Need to disconnect and reconnect."

Other WiFi vendors designed their units to be interchangeable, router or access point.  Same hardware.  Just a different setting in the software.  Netgear did not.  (And... we often stick pins in our "Netgear Engineer Doll" hoping that this bozo feels our pain.)