Displaying custom module form results Drupal 9

I have created a custom module that pulls in data from an external API, a user selects a few filters on a form and submitting the form makes a call to the external API.

This works, but the only way I can display the results is by using Drupal messanger:


But this isn’t the right method for displaying content I’ve found a few other suggestions but I can’t get any of them to work, all are for older versions of Drupal.

I’d like to be able to display formatted results under the form on the same page, how do I do this in Drupal 9?