When adding Sequences 1.0.0-pre.5, the 2021.2 alpha20 breaks with
Library\PackageCache\com.unity.sequences@1.0.0-pre.5\Editor\Startup\SetupMasterSequenceDragAndDrop.cs(32,35): error CS0426: The type name 'HierarchyDropMode' does not exist in the type 'InternalEditorUtility'
Considering one of the patch notes for a19 was Package: Added com.unity.sequences 1.0.0-pre.5 package.
, I’d assume this is a regression.