No content in trash bin

Is the problem happening on a fresh Drupal install or an existing site with other modules installed?

Existing site with other modules.

In that case, some debugging is needed. First, I would look at \Drupal\trash\TrashStorageTrait::delete() and check if it's immediately going to the parent delete method, which means the trash context is not active. If that's the case, the next step is to put a breakpoint in TrashManager::setTrashContext() and see who's changing the trash context.