Iphone XS max WiFi connection problem with specific network

All other devices incl. Ipad 's laptops several other iPhones here in the house can login to this specific WiFi network only my fairly brand new Iphone XS Max can't. Tried all the usual remedies available: Toggling WIFI on/off, resetting Network settings, system location settings on/off etc etc. and of course restarted the iPhone about 10 times at least, restarted router and its extensions --- nothing did the trick. If anyone out there has an idea - please reply. Your help will be greatly appreciated. Many thanks in advance. (And yes the system is fully updated.)