I have created this app flutter with Rest API, API is open source.
Youtube Tutorials: https://youtube.com/playlist?list=PLFyjjoCMAPtzgITDreXNNkSWLKbd1wf51
This app has the following features.
Track whole world covid states Show overall states in Pie Chart Display countries list with active case Filter countries list Track covid states countries wise
You are welcome to modify the source code and make it usable according to your own requirements.