iMessage banner will not go away

Actually you can toggle it off or change it from Persistent to Temporary in

Settings > Notifications > Messages > ALERTS > Show as Banners

If you're talking about Previews, you can change that from Always to When Unlocked or Never in

Settings > Notifications > Show Previews but that affects all applicable apps

Toggle it off within Messages Notifications settings under ALERTS.

Settings > Notifications > Messages > ALERTS > Show as Banners

Hi

Try a reboot press the power button down &menu button hold both down until you see apple logo this can take 30 seconds.

Cheers

Brian 🇬-1F1E7;