Is there any possible way to add the custom created jar plugin to SonarQube in UI?

I have created a custom rules java plugin jar and able to add this in extensions/plugins folder and restarted the server. is there any possible way I can do it in UI directly?

There is no way, that you can directly upload a plugin to sonarqube. If you want to make it wide available, you can always try to make the plugin available on the Marketplace.

The question is always, what is your usecase. Are you developing a company internal plugin. Is it an Open Source Plugin worth adding to the Marketplace. What instances of Sonarqube do you want to install it on. I can imagine, that you could theoretically also manipulate the response of the Marketplace in a proxy to add your plugin, but therefore you would need again infrastructure access, and most likely if you have that it is easier to just upload it to the sonar server directly.