Use CSP to control the sources from which content can be loaded on your website, including scripts, styles, and frames. Define a strong CSP policy to prevent unauthorized framing and loading of external resources. Example in HTML meta tag:
<meta http-equiv="Content-Security-Policy" content="frame-ancestors 'self';">Source: Clickjacking/README.md in PayloadsAllTheThings. From PayloadsAllTheThings by Swissky and contributors. MIT License, Copyright (c) 2019 Swissky.