Hello @lolix3 ,
You can have a deepdive into WindowsUpdate FAQs here: https://support.microsoft.com/en-us/windows/windows-update-faq-8a903416-6f45-0718-f5c7-375e92dddeb2
But in my experience the main difference is: Windows will push via Automatic updates, the recommended updates for your system, programs and drivers; while manual check will show you all available updates for your system for you to check.
Best regards,