Verify the most important settings.

In the Identity section of the General tab:

The display name of your app.

The App ID you registered on App Store Connect.

In the Signing & Capabilities tab:

Whether Xcode should automatically manage app signing
and provisioning.  This is set true by default, which should
be sufficient for most apps. For more complex scenarios,
see the Code Signing Guide.

Select the team associated with your registered Apple Developer
account. If required, select Add Account…,
then update this setting.

In the Deployment section of the Build Settings tab:

The minimum iOS version that your app supports.
Flutter supports iOS 11 and later. If your app or plugins
include Objective-C or Swift code that makes use of APIs newer
than iOS 11, update this setting to the highest required version.

The General tab of your project settings should resemble
the following: