How do non Cox guests use my WiFi is the gateway won't allow a guest network?

I do have a panoramic wifi modem too, but I used these ethernet ports to daisy chain my secondary router.

Here's what I did:

First, I configured my unused Linksys wifi router.

Next, I attach an ethernet cable to my panoramic router's WAN ports below 2 phone jacks.

Next, I test my secondary network to confirm if my router is working.

Next, I tested my guest network what I've implemented. I set my secondary router name with a "Guests" suffix after an underscore symbol.

I replaced my Linksys's firmware with DDWRT to get the most from my router.

I've also set my router to a specific location of my apartment.

Do you really have a secondary router what you can use to expand your network.