As a beginner, I learned HTML5, CSS3, Bootstrap, and JavaScript? What should be the next thing I learn to become full stack web developer?

Answer 1

Responsibilities for full stack developer covers but not limited to front-end, back-end, and database work.

Looks like you have learnt front-end technologies. Next thing will be learning back-end and database.

Java and C# are pretty famous object-oriented programming languages for back-end work.

Also for the database there are relational(MS SQL) and NoSQL(CosmosDb) databases. I would suggest you to learn MS SQL.

Hope this helps!