

The overview: environment, what is running, and what has changed recently.
The usual way to find a plugin conflict is to deactivate plugins one at a time and see what changes. On a live site that means taking features away from real visitors and customers while you experiment.
TroubleLens does the same investigation without that cost. It gives you a private troubleshooting session: plugins you switch off stop loading for your requests only. Everyone else — visitors, customers, other administrators, search engines, scheduled tasks — continues to get the site exactly as it is. The list of active plugins in your database is never changed.
Starting a session writes one small must-use plugin and sets a cookie in your browser. On requests carrying that cookie, WordPress is told a different list of active plugins. That is the only supported way to do this: the plugin list is read before any normal plugin has loaded, so the code doing the filtering has to already be running.
This is a diagnostic tool, so it does not change things it is measuring:
active_plugins option, and it prevents anything else from writing it while a session is running.wp-config.php, including to enable WP_DEBUG.TroubleLens has no telemetry, no tracking and no advertising, and contacts no third party service. The HTTP requests it makes go to your own site and nowhere else: to your REST API, to check that it answers, and to your own pages, to time them or to see whether a symptom is still there.
There are exactly two exceptions, and each only happens when you press the button that causes it.
The outgoing mail check sends a single message to the email address on your own account, so that a site whose mail is broken finds out before its customers do. It carries nothing about your site beyond its name.
The core file check asks WordPress.org for the list of checksums published for your exact version, and compares the files here against it. All it sends is the version and language needed to identify which list to return. Your own themes, plugins and uploads are never checked, because nobody publishes checksums for those.
Support reports are built and rendered on your server. Nothing is transmitted anywhere; you copy or download the report and send it yourself. Before it is shown to you, passwords, salts, authentication keys, tokens, API keys and payment gateway credentials are removed, email addresses are replaced, and absolute server paths are made relative.