As support side on tp-link products is non existent and no software updates are provided, I had to buy an Zyxel device, that is working without problems on N1 5G with speeds up to 250 down and 100...

Enable the option "5G only" under Internet -> Network mode, as indicated in Configuratio Guide for Deco X80-5G. This guide (https://www.tp-link.com/en/support/faq/3078/) has screenshots, so why only...