wifi 6.0cant connect to it xfinity unable to solve

got new xb8-t modem have a few devices that require 2.4 signal so ive never used band steering .so i have diff name for my 2.4 5.0 and now was stoked to try out this wifi 6.0 .i can not get 1 device to connect to the 6.0 xfinity techs cant help very frustrating .even tired using one name for ssid .....nope not 1 device ,iv checked my devices to make sure whats compatible .fyi  when i used 1 name the modem put both my iphone and ipad pro on the 2.4 with sitting 2feet away from it .please help if can