iOS 15.6.1 network issues cellular and wifi

IPhone 12Pro on iOS15.6.1 (latest version) - now my phone seems to randomly disconnect to cell network or WiFi - apps keep showing internet connexion error. phone shows its on 5G but if you swipe down, Wifi shows its on and connected. no internet connexion. Switching off WiFI sometimes enables 5G connexion but that doesn't last long, it 'disconnects' and same error