Hi Guys, I am planning to get Deco x20 and wonder if I use my current re 705x entender in Deco's mesh ?

Recently I bought re705 extender and now part of to one mesh but can't see big benefit. What should I do ? My Vdsl modem archer vr400 and i wonder making re705 a hot spot too see my devices doing bett

my Archer 400 came with wifi 5 and I also have rx705 which has wifi 6 in the same oneMesh, I wonder if there is any way I can disable wifi 5 on vr400 and plug in USB wifi 6 stick that might upgrade to