In MongoDb 5.0 release the isMaster command was renamed to hello, and when we try to stream cdc from mongo 4.0.12 we get a timeout exception for the 
MongoUtils.hello(client, dbName);
So I have added a try-catch block to try both ping commands (hello and isMaster)

Bug report

Found a way to extend support for mongoDb version 4.x

What Debezium connector do you use and what version?

MongoDb Source Connector 

What is the captured database version and mode of deployment?

4.0.12 on AWS EC2

What behavior do you expect?

Extend CDC capture from this mongo version

What behavior do you see?

Unsupported

Do you see the same behaviour using the latest released Debezium version?

Yes, 2.7

Do you have the connector logs, ideally from start till finish?

(You might be asked later to provide DEBUG/TRACE level log)