Neovim 0.10 was the longest release cycle since the heady days of the 0.5 release. There are a ton of new features in this release (as well as some breaking changes), so be sure to check the full release notes. You can view the release notes directly in Nvim with :h news. The news file includes information on new features, deprecations, and breaking changes. I especially urge plugin authors to read this file carefully.