Configure GL.iNet GL-BE9300 (Flint 3) on KPN fiber

Backstory Up until a few days ago my main Wi-Fi router was an Apple Time Capsule. It's one of the latest models but still this thing is old . Apple discontinued the product line in 2018 but I probably bought it in 2013, maybe 2014. That makes it over 10 years old. It survived 3 NYC apartments, a move back to The Netherlands, being stored in an attic for a while, dusted off and then 2 more houses.…