Business.site is a part of Google's My Business (now called Google Business Profile) service, allowing businesses to create a free, basic website that integrates directly with their business profile on Google. It's designed to help small businesses establish an online presence easily and is tied specifically to Google's ecosystem.
.Site is a new top-level domain extension (gTLD) which is used by Google's Business.site as their domain and is available for anyone to register. Unlike Business.site, which is a service, .site domains can be purchased and used for any purpose, ranging from personal websites to business portals.