If you have already learned Angular then i would suggest that you learn MongoDB and then you can move on to NodeJS and then ExpressJS. This would allow you to learn MEAN Stack. Learning MEAN stack is a good idea because in MEAN Stack you can use your JavaScript logic to build both the front-end and the back-end of the application that you wish to build. You can also learn to use react however i don't see any benefit in that since react and angular are both frameworks for building front end of an application and you already know angular.
You can read this blog that explains what MEAN stack is.
To learn full-stack development from experts, enroll in this Full Stack Web Developer Course offered by Intellipaat.
You can learn MongoDB by following these tutorials, or you can watch this video to learn more about MongoDB
You can also get certified in MongoDB, by enrolling in this MongoDB Online Certification Course.
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