Thanks not to have been rude. But I’ll try to help other guys with my same problem, given I’ve solved it in 10 minutes with chatGPT.
Full 6GHz from my Quest 3 to my laptop, through the Arris W3B only. Yes, not a catch 22 this time.
So:
(1) I directly connected my W3B to my Win11 Pro laptop ethernet port (2.5Gbe), looking at the IP that my laptop DHCP assigned to the Arris (192.168.1.70). Why should have I used an external router? Windows can perfectly use its DHCP function.
(2) in the W3B web panel (accessible through 192.168.1.70) i did enable the SID, selected the HT160 wide band and PSC 101 (the highest allowed 6GHz channel in Europe - so to be on the safe side)
(3) optional pass: in my Windows network properties I enabled internet sharing for my Wifi adaptor (so that the Quest can access the web through the Arris, that inherit the internet from the PC’s wifi)
(4) In my Quest 3 I connected to the Arris wi-fi SID, and easily verify (latest Meta OS, July 2025) that the used band is 6GHz: bingo!
After having restarted the Meta Link, everything works perfectly in AirLink.
Long story short: YES, you can use the W3B as a W3U for a Quest 3.