it's been a few years since working with Jira, so I'm playing catchup a little...
I'm currently working with Jira Data Center version 8.22
I've noticed a 'Plans' top-level menu item.
I see nothing under 'Manage Apps > Manage Apps' which suggests this isn't a plugin.
Also, a quick look online and it seems that 'Porfolio for Jira' was rebranded 'Advanced Roadmaps' (which I'm presuming is what's rendering the 'Plans' top-level menu) <-- can someone confirm this?
Also, from what I can tell from the documentation, Portfolio for Jira / Advanced Roadmaps / Plans is now part of Atlassian's Jira offering since v 8.19 so is covered under the Jira Core and/or Jira Software license - am I right?
Advanced roadmaps is automatically included with Jira Software Data Center from 8.15 and beyond. Since you are running on 8.22 you have got it natively in your instance.
Atlassian has rebranded Portfolio for Jira as “Advanced Roadmaps” as of May 13, 2020, so yes it renders the "Plans" in the top level menu.
You will find the app listed under "Application components" under Manage Apps.
You are correct in that the cost of Advanced Roadmaps is covered under Jira Software License.
Hope this helps.
As stated by @Kishan Sharma , the basic concepts and functionality are the same even it is now named "Advanced Roadmap for Jira". The configuration for the setup via Manage Apps UI (left pane), you will still find
The key information that you need to be aware of is that "Live Plan" will be decommissioned, all plans will need to use the new improved UI. Please this article - https://community.atlassian.com/t5/Advanced-Roadmaps-articles/Ending-support-for-the-Advanced-Roadmaps-Live-plans-Legacy/ba-p/1963824?utm_source=atlcomm&utm_medium=email&utm_campaign=immediate_general_article&utm_content=topic
Hope this helps.
Best, Joseph Chung Yin
Jira/JSM Functional Lead, Global Infrastructure Applications Team