Found under Tools in the dashboard, it has a Status tab that lists critical and recommended items, such as an outdated PHP version, inactive plugins or a failing background-update test. Its Info tab shows environment details including versions, constants and paths.
Site Health is a helpful early warning, especially for automatic updates, but it is not a malware scanner and it does not prove that a site is patched or clean. A green result means only that its limited checks passed.
The Info tab can reveal server details that should not be posted publicly, so review and redact it before pasting it into a forum or support ticket.