The "related concepts" section under the whiteboard gives you several types of suggestions related to what you have on your map.
Personal: related ideas from previous maps created by you
Topics: related topics
Community: related ideas shared by the community
Trending questions: questions people type in search engines
Keywords: keywords people type in search engines
You can choose which type of suggestions you want using the funnel button as shown in the screenshot below.
Filtering suggestions in text search
The same filter works also for text search when you are typing the name of a new concept, as shown below:
Loading more suggestions
In both cases, you can keep asking for more suggestions by clicking the "Load more" button at the end of the scrollable list.
Watch how it all works in the video below: