I'm trying to connect an old RBS50Y in extender mode to the RBRE960

Jiheffe2 wrote:

Does this RBRE960 - RBS50Y work? I read something about Orbi AX above? What are these?

Yes, the RBS50Y in Extender Mode should connect to any WiFi router from any brand.  "AX" is used in the Community Forum to describe Netgear's WiFi6 routers.

What happens when this suggested procedure is used?

https://www.downloads.netgear.com/files/GDC/RBS50Y/RBS50Y_QSG_EN.pdf

i.e. Ensure that the RBS50Y is in Extender Mode, place it close to the router, and use the Sync buttons to connect.