How far is the Timberline from your WiFi router or nearest access point.
Does your router use the same SSID for both 2.4 gHz and 5 gHz bands? Many routers are set up that way so devices can easily switch from one band to another depending upon signal strength. However, in order to set up the WiFI on the Traeger, both your cell phone and the Traeger must be connected to the 2.4 gHz band. If the same SSID is used for both bands, it is likely that your phone is connecting at 5 gHz and you won't be able to connect the Traeger. You have one of two options.
You can go into the router settings and establish separate SSIDs for each band. Note that some router brands, especially those with mesh systems do not permit that.
The second option is to go into your cell phone settings and disable the 5 gHz radio such that it has to use the 2.4 gHz band. You first have to connect the Traeger to the cell phone using Bluetooth and then the WiFi settings are transferred from your cell phone to the Traeger.
If you disabled the 5 gHz radio on your cell phone, don't forget to turn it back on after getting the Traeger set up. I would also suggest going into the DHCP settings of your router and establishing a DHCP reservation for the Traeger controller. That is not a necessity, but it might be helpful.