The S21U was very spotty with connecting to 6E. It would only see it on a router reboot. I thought it was more the router than the S21U, however my laptop would solidly connect to the 6E network, so it must have been the S21U. Since I'm on WiFi7 with the S24U, I haven't kept track of it. I will flip over and check it out later.
Wi-fi 6e missing (6 GHz on one of two ultras). Perhaps coming from an app? Wifi analyzer can see the 6ghz, just can't see them to connect. May try wifi reset, although communications reset could have been the source of this problem. Others have reported it, so not an isolated issue.
Edit: Fixed: Rebooted into safe mode. Wifi 6e worked. Normal boot back. No wifi 6e in available nerworks. Unistalled Asus Router app. Checked for Wifi 6e being visible in wifi available networks. Nothing. Deleted Netgear Genie app. Then saw networks. of mine I had not connected to in wifi available networks. Forgot the desired 2.4&5&6 SSID that did not show 6E. Connected to it again. 6e now works.