wpForo theme files contain the markup and template structure for the frontend of your forum. Theme files can be found within the /wp-content/plugins/wpforo/themes/ directory, in current active theme folder, for example /2022/.
You can edit these files in an upgrade-safe way using overrides. Just create /wpforo/ folder in your current active WordPress theme directory /wp-content/themes/yourtheme/, and keeping the same folder/file structure.
Example: To override the “Topic List” template file of the Extended (#1) forum layout, copy:
wp-content/plugins/wpforo/themes/2022/layouts/1/topic.php
to
wp-content/themes/yourtheme/wpforo/layouts/1/topic.php
The copied file will now automatically override the wpForo default theme file. All changes in this file will not be lost on forum update.
IMPORTANT: Do not edit these files within the core plugin itself as they are overwritten during the upgrade process and any customizations will be lost.