If you have changed host or upgraded from old version to new version,
there is a chance that, you will not be able to “add new plugin” option in your self hosted wordpress admin dashboard.
after searching for more than 2 hours, i come across solution for it.
Solution is very simple,
Go to PhpMyAdmin,
Select your wordpress database,
go to wp_options table
and find `db_version` and replace its value with 8204
Now if you go wp-admin, it will ask you to upgrade your database
and voila! now you can see “add new plugin” option.