Steam previously announced that starting January 1, 2024, it will no longer support Windows 7, Windows 8, and Windows 8.1. As this cutoff date is rapidly approaching, users of these older operating systems are strongly encouraged to update to a newer version of Windows.
Continuing with outdated systems poses security risks, as they will not receive updates, including vital security patches. This shift is necessitated by Steam's use of Google Chrome, which doesn't support older Windows versions. For complete functionality and security, upgrading is essential.
For more details, please refer to Steam's announcement here.