5Ghz
How can I connect my IphoneXR to a 5Ghz WiFi signal ?
iPhone XR
Check your WiFi Router / Modem for --> Recommended settings for Wi-Fi routers and access points ...
Please check what does your router supports
From your question I presume that you know this --> Wi‑Fi 6 (802.11ax) replaces Wi-Fi 5 (802.11ac), which in turn is replaced with Wi-Fi 4 (802.11n) as the standard for Wi-Fi speed in 2013
The iPhone 11 and later is capable of connecting to Wi‑Fi 6 (802.11ax) both 2.4 GHz and 5 GHz
The iPhone XS has Wi-Fi 5 (802.11ac) which only supports 5 GHz
Wi‑Fi 6 (802.11ax) supports both 2.4 GHz and 5 GHz. But 802.11ac (Wi-Fi 5) only supports 5 GHz.