On March 6, QGIS version 4.0.0, codenamed “Norrköping”, was released. From the announcement:
On the surface, existing users should expect to engage with a GIS experience familiar to what they have come to know and love from previous QGIS releases. Under the hood, however, it introduces significant changes to maintainability and usability. These changes ensure that QGIS 4.0 can unlock additional access to modern libraries while bringing much-needed performance and security improvements to the codebase.
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While preparation for the QGIS 4.0 migration has been underway, the developer community has added over 100 new features across the application, making QGIS more powerful, more flexible, more secure, and generally just more awesome.
In a major update to the underlying application framework, QGIS 4 is built on Qt6.
As to other improvements, some highlights are listed on the release page (scroll down). And there is a longish (23 minutes) “visual changelog”, essentially a video showing new features: