Ok, second acceptable option form me is not to use else but default code path. Like this:
		if (count($tmp) >= 2 && $module = strtolower($tmp[0])) {
			if (isset($files[$module])) {
				return $module;
			}
		}
    
		return $files[0];
Is this better from your point of view?

Next option is somewhat complex if statement, but it is harder to understand form my point of view.