RBR50 - cannot open the ADMIN site using Chrome or Edge (or certificate warnings)

Actually, the latest firmware is v2.7.5.4. https://kb.netgear.com/000065539/RBR50-RBS50-Firmware-Version-2-7-5-4 which was released Feb 23, 2023.  If you ever get access to the router, it can be manually installed (satellites first).
(Totally your choice.)

Not finding the IP address would happen if the laptop were connected to the Guest WiFi network rater than the primary WiFi network. (Easy to check.)

The warnings and security notifications are an awkward issue as a result of modern web browsers having implemented new protocols to "protect" users:

• Accessing the unencrypted (http) web site prompts the "insecure" warning as it does for every attempt to access any http web site.  Knowing that (a) I am on my own LAN and (b) I am 100% certain that this IP address belongs to my router, I simply direct the web browser to proceed to the web site and it remembers this for future connections.  (If a Google search for "space alien parts" took me to an unencrypted web site, I might think twice about ignoring the warning.)
• Accessing the encrypted (https) web site prompts a warning that the SSL certificate is self signed, which it has to be.  Up until about 3 years ago, Netgear had registered several URLs and got a signed certificate. (routerlogin.com, orbilogin.com, orbilogin.net, and several others).  That SSL certificate was not renewed, possibly because those thousands of web sites are not actually run by Netgear (but by thousands of customers all around the world).  Netgear began shipping a self signed SSL certificate with their routers.  Once again, (a) I am on my LAN, and (b) I know that this IP address is my router.  So I direct the web browser to proceed to the IP address.  (If a Google Search led me to a web site that had a self signed SSL certificate, I would perhaps wonder, "why didn't they get a real certificate?")

In short, no one can stop Chrome and Edge (based on Chrome) from complaining about the Orbi web site.  I use Firefox or Opera.  Eventually they may also activate those user protections.

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