Last night Apple auto-updated my iPhone 8 Plus and installed iOS 15.5. I've gone through many such updates for years with no problems. Beginning today with the first use of my iPhone, the WiFi connection dropped repeatedly. I went to Settings and turned WiFi off and then back on and reestablished a connection, but it lasted only a short time -- maybe 15 seconds -- and then dropped again.
I've tested all other devices served by the router and my updated iPhone is the only one with this problem.
Router is ASUS RTN66R Double 450 Mbps N Router. Serving 6 devices.