@Clem_Viking The web interface is different, because I used another TP-Link device just as an example - you didn't mention what model is your DSL router. In your Internet connection=>Advanced...

@nrajeshgoud Change this setting and check if that makes any difference:

@Vijaya01 Login your router web management interface via browser at http://tplinkwifi.net through the 5GHz band (or ethernet cable) and enable the 2.4GHz band again:

@Clem_Viking What you're referring as "'a tick box labeled 'use ISP supplied DNS'" is in the Internet connection settings=>Advanced (for example): The screenshot you posted is your LAN DHCP server:...

@DennisSSebasiSt You could buy a cheap dual band wireless router like Archer C64 or similar and connect it behind the ISP modem. Before taking any action consult with your ISP if their modem can be...

@RainSong Glad you've made it, stay safe !