You can try to compare the app version number via GetDeviceInfo (NativeMobileResources) and compare with a constant that is updated on the Environment.
This should be done just after launching the app, before sync.
If is different, you could redirect to a page with the message "please update to the latest version"
see also:
https://www.npmjs.com/package/react-native-device-info#getversion
https://reactnative.dev/docs/platform#version
Use the Mendix API to retrieve the current version of the model of your environment. See documentation here: https://docs.mendix.com/apidocs-mxsdk/apidocs/deploy-api/#list-environments
This way you can retrieve the current version of your model and compare it to the mobile version.
Regards,
Ronald