Dual router - can't get it to connect to 5ghz

5GHz radio mode

This setting controls which versions of the 802.11a/b/g/n standard the network uses for wireless communication on the 5GHz band. Newer standards support faster transfer rates, and older standards provide compatibility with older devices and additional range.

Set to: Auto or 802.11n/ac

Routers that support 802.11n should be configured for 802.11n/ac mode for maximum speed and compatibility. Different Wi-Fi routers support different radio modes, so the setting varies depending on the router. In general, enable support for all modes. Devices can then automatically select the fastest commonly supported mode to communicate. Choosing a subset of the available modes prevents older devices from connecting. For example, 802.11ac devices can't connect to a Wi-Fi router in 802.11n-only mode. Also, choosing a subset of the available modes might cause interference with nearby legacy networks, and nearby legacy devices might interfere with your network.

Recommended settings for Wi-Fi routers and access points - Apple ...

https://support.apple.com/en-us/HT202068

The ability to connect to 5GHz versus 2.4GHz is based on what the router is set up to identify. You should have a separate SSID for the two bands, which would then help the iPhone identify the two. Since you mention IT, is this some type of business router? My personal home router has settings for both bands, and you can set a separate SSID to help you identify the two bands and connect. The iPhone XS Max should have no difficulty connecting to a 5GHz wi-fi, I use 5GHz for my iPhone XS, iPad Pro, and MacBook Air now, and used it for my iPhone X. I would check back with IT to see why they do not have separate identifiers for the 2 bands.