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How do I find out what is in control over a certain part of a website?

I’ve been trying to get myself familiar with WordPress but with a Joomla mindset I find it quite hard.
In Joomla, when you are trying to find out what is in control over an area, you just need to find out what position it is and then you can easily find out whether it is a module or a component.
But in WordPress things are totally different. For example, on this site:https://fedlearningcenter.com/ which I am trying to remake for learning purpose and know that it is built using BuddyBoss, after I login, the customer login area will be like this screenshot
enter image description here

Although I know this area is built by Buddyboss, I still don’t know how to make it. It is in the navigation bar, it could be a widget(unlikely but still possible, isn’t it?), it could be controlled by the theme, it could be controlled by a page builder, it could even be controlled by some other plugins that could affect the navigation bar. Then how do I find out who is really in control and connect my Buddyboss’s setting with it?

P.S.: My question is not just about Buddyboss. My question is about understanding how wordpress manages elements on a page on a more basic level.