Have just set up my new Hub 4 and received a message from Microsoft that the router is not secure and the wifi network is an older security standard that is being phased out. Advised me to use another network
So you must have standard (ADSL) broadband then.
The HH4 does support WPA2 on 5Ghz, which should be fine, so I would not worry about it.
2.4GHz is just WPA which is an older standard.