1. Try to get rid of every mods with this icon. Each of them has got a outdated "Mod Fixer" which just prevents you from starting a new game after Patch 7.
2. Get the latest ImprovedUI Patch7Ready(https://www.nexusmods.com/baldursgate3/mods/366), and the weird dialog box would disappear.
Doesn't need to reinstall the whole game I think.