Question about ASUS GT-AX11000 Gaming Router WiFi 6

Yes, that's possible, I did it too. Depending on whether you configure it as a direct router or as an access point, you can plug it in via the WAN or the normal LAN connection. If you have the new Swisscom router, you can also use the 2.5G connection.
I don't know if a network specialist will correct me right away that one method is never used, but it works in any case in all these ways.