Kivy

I want to start working on mobile applications with Python, which tool do I need to consider with PyCharm, Kivy, or Flutter?

We are developing an AWS IoT app for large boats. The IoT devices have sensors all over the boat for engine oil pressure, position, water depth, fuel level, crew location, etc. When the boat has internet, we interact with AWS cloud using lambda and Amazon DynamoDB. When the boat is offshore, the captain and crew still need normal and emergency alerts and real-time sensor information. The crew might have an Android or IoS phone or a Windows or macOS PC to receive alerts and interact with sensors. We may use the AWS GreenGrasss edge computing solution and either MQTT or HTML for that function.

Question: We want to develop a cross-platform client to run on Windows, Mac, Android, IOS, and possibly Linux. We are primarily Python programmers, so PyQt or Kivy are options for us, but we have heard good things about React Native, Flutter, Xamarin, and others. We think an AWS Greengrass core on an RPI4 could communicate to the client with MQTT or a local webserver with a client web interface.

Any thoughts would be much appreciated.