Single item: Topic

You can create a custom template for the Topic post-type using the Site Editor by following these steps:

1. Navigate to Appearance > Editor.
2. Click on Templates under the Design column and then click the Add Template button.
3. In the popup, choose Singe item: Story.
4. On the next screen, pick either Stories to apply the template to all stories or Story to apply it to a specific story.
5. Select an existing pattern and customize your new template as needed.
6. Click the Save button to finalize your changes.

Please note that if the selected pattern utilizes the Categories block for displaying a list of the assigned category terms for this topic, make sure to transform this block and select Forums, as demonstrated here:

Also, if the selected pattern utilizes the Post tags block for displaying a list of the assigned post tags for this topic, make sure to transform this block and select Topic Tags, as demonstrated here: