I believe you can just turn off the WiFi radios under Gateway, Connection, WiFi, see screenshot.  

Hi hope you are doing great,

On the Web Manager of yout SBG8300, On the menu at your left you can go to Gateway> Connection> WiFi,

Right there you will find the WiFi Radio Controls 2.4 and 5G, to Enable or Disable them

is always recommendable to make this setup while you are hardwired to the Gateway for a better application of the changes.

Also this articles can help you out

https://arris.secure.force.com/consumers/articles/General_FAQs/SBG8300-Changing-the-Wi-Fi-Name-and-Password/?l=en_US&fs=RelatedArticle#:~:text=Under%20the%20Home%20Wi%2DFi,in%20the%20Network%20Password%20field.

https://arris.secure.force.com/consumers/articles/General_FAQs/SBG8300-Disable-Guest-Wi-Fi-Network/?l=en_US&fs=RelatedArticle#:~:text=The%20Gateway%20%3E%20Connection%20%3E%20Wi%2D,for%20the%20Wireless%20Network%20option.

Siuu1994

For the SBG7600AC2, those pages are different.  When I go into the admin application, I can select, on both the Wireless 2.4GHz and the Wireless 5GHz tabs a checkbox that says “Enable Wireless”.  If I uncheck that, is it the same as disabling the Wifi radio in the picture above for the SBG8300?  I’m trying to connect my modem/router to an eero for mesh network coverage in my 1800 sq ft house.  I tried Bridge mode this morning but had a problem - contacted eero support as well.