SharePoint Online, as part of Office 365, is continually improved. The SharePoint Help Center is also continually updated with the latest changes. Below are some other resources on what's new.
SharePoint updates on the SharePoint Community Blog
Read the SharePoint Community Blog anytime to learn best practices, news, and trends directly from the SharePoint team.
Two recurring updates on the SharePoint Community Blog specifically highlight what's new.
The Intrazone is a show about the SharePoint intelligent intranet.
The SharePoint Roadmap Pitstop is the comprehensive, consolidated recap for all things SharePoint to keep you up to date.
SharePoint updates on the Office Blog
Microsoft 365 Roadmap
The Microsoft 365 Roadmap is the official site for Microsoft 365 updates and changes, including Office 365. See what's in development, rolling out, and launched.
Administrators and IT Professionals should read Stay on top of Office 365 changes which covers how to configure update messages delivered through the Microsoft 365 admin center.