Html injection in Activity and just only need html payload in workflow and fire in Activity list
<h1>test</h1>
POC:
https://drive.google.com/file/d/1yDznjYdHFZ4WJNRk8LEHlZhvonyghZQE/view?usp=sharing
https://drive.google.com/file/d/1kBA8oF-SaMVI8aVkM39Ora8GBdDvKjIT/view?usp=sharing