DIAGNOSIS The TV's Wi-Fi module is likely set to a channel width or DFS channel your router uses for 5GHz that the TV does not support. The Bravia's wireless chip has compatibility restrictions.
FIX Log into your router's admin panel. Navigate to the 5GHz wireless settings. Change the channel width from 160MHz or 80MHz down to 40MHz. Also, manually set the control channel to a number between 36 and 48. Save settings and restart the router. On the TV, go to Settings > Network & Internet > Set up network connection. Select your 5GHz network and try connecting again.
IF THAT DIDN'T WORK A firmware mismatch can cause this. On the TV, go to Settings > System > About > Software update. Select System software update and ensure it's fully updated to the latest version. Retry the connection after the update installs and the TV restarts.
HEADS UP The TV's Wi-Fi does not support WPA3-only security. If your router is set to WPA3, you must change it to WPA2/WPA3 mixed mode or WPA2 Personal for the TV to connect.