Is there a way to generate the javadoc for a method by typing "/**" in VSCode just like in Intellij?
Intellij automatically writes annotations like parameter and return value.
Yes there is, and it should be working for you (if it's not, then you're likely encountering a bug).
Here's the feature request issue ticket that requested that this feature be added:
https://github.com/redhat-developer/vscode-java/issues/228.
Here's the Pull Request that implemented it:
https://github.com/eclipse/eclipse.jdt.ls/pull/744.
Here's a bug report reporting that it stopped working that got resolved as fixed:
https://github.com/redhat-developer/vscode-java/issues/811.
If it's not working for you, read through those threads and see if your issue is related to the Intellicode extension. If not, revive that third link I sent with details to reproduce your issue and logs.
As clarified in the comments, the issue was that the asker had two Java language server extensions installed. After uninstalling one of them (georgewfraser.vscode-javac), their issue was resolved.