@Alexandre. tried this already, both guest network and normal to 2,4ghz only, no luck. Just sounds weird if you are not able to change the ax to ac mode, you can do that on the Archer AX50 i own, and...

I own a 3pack X20 Mesh network, this version: https://www.elgiganten.dk/product/computer-kontor/netvark/router/tp-link-deco-x20-mesh-wi-fi-6-kit-3-pak/150297#specifications I own a Lenovo Yoga 3 14...