The plugin `fluttertoast` uses a deprecated version of the Android embedding.

-The plugin fluttertoast uses a deprecated version of the Android embedding.

问题描述

`The plugin `fluttertoast` uses a deprecated version of the Android embedding.`To avoid unexpected runtime failures, or future build failures, try to see if this plugin supports the Android V2 embedding. 
Otherwise, consider removing it since a future release of Flutter will remove these deprecated APIs.
If you are plugin author, take a look at the docs for migrating the plugin to the V2 embedding: https://flutter.dev/go/android-plugin-migration.

 fluttertoast: ^3.1.3

原因分析：

fluttertoast插件使用的是Android内置的一个弃用版本。
为了避免意外的运行失败，或者将来的构建失败，试着看看这个插件是否支持Android V2嵌入。
否则，考虑删除它，因为Flutter的未来版本将删除这些已弃用的api。

解决方案：

打开Terminal
输入一下代码，升级插件

flutter pub upgrade --major-versions

将插件升级到最新版本
如下，将fluttertoast的3.1.3版本升级到8.0.9

Pub get 成功