Here is my GTM Configuration for an event.
Now I want create a report in GA4, were I can see in rows the values of popular_categories with event count for that value. How can I do that? I have already about 1000 clicks with Popular Categories Event. I can see it under Property Configuration -> Events. But in my report I can see only Popular Categories event count and not the event parameter values.
First, per GA4's event naming rules, I recommend changing your tag's event name from Popular Categories to popular_categories_link_click.
Then, you'll need to create a custom dimension to start seeing data for your popular_categories event parameter.
To create the custom dimension,
Custom dimensions are not retroactive, so you'll only be able to see popular_categories event parameter data from this point onward.
To see this data, use a Report or Exploration with: