After upgrading flutter version its want to sdk also update pubsec yaml sdk: ^3.6.0

take backup your android,ios folder then delete that

flutter create . (it will generate your android ,ios ,web and others as well)

check your manifest file it will comes as its then run if its shows error midsdk 34 like change as per your project need it will solve issues

sometimes the app size will big.

ANOTHER WAY: If your working local projects create new project copy paste your lib folder to new project same as well add your pubspecyaml also. It is simple way to solve issues.