GHWatcher collects nothing about you, has no account and no server. It talks only to GitHub, with a token you give it. This page covers the Mac and Windows versions.
Your GitHub token. The personal access token you paste into Settings is kept in the Mac's Keychain, or in Windows Credential Manager under TKG GHWatcher/github-token. It is never written to preferences, logs or files. Remove token in Settings deletes it.
Your preferences. The refresh interval, which notifications you want and whether to start when you sign in. On the Mac they are stored in the app's own container; on Windows in settings.json in your user profile's app data folder (TKG GHWatcher).
Besides the token and the preferences above, the Windows version writes three small things for itself, all under your user account and none of them containing data about you:
ghwatcher: link);Requests to GitHub's API (api.github.com) and nothing else. Your token goes with them so GitHub can answer which pull requests, reviews and checks are yours. GitHub's own privacy statement covers what GitHub does with those requests. Notifications are shown by your own computer; nothing is sent to a notification service.
Pull request data is fetched into memory to be shown and dropped when the app quits. GHWatcher keeps no copy of your repositories, code, commits or pull requests, on your computer or anywhere else.
There is no telemetry, no crash reporting of our own, no identifier, no advertising and no third-party SDK. If your operating system asks whether to share a crash report with its maker, that is the system's mechanism and your choice.
Click Remove token in Settings, then delete GHWatcher (on the Mac, from Applications; on Windows, uninstall it). On Windows, Credential Manager keeps its entries when an app is uninstalled, so remove the token in Settings first — or delete TKG GHWatcher/github-token in Credential Manager afterwards. You can also revoke the token on GitHub at any time.