Similar to the idea of hotizontal tabs but in vertical.
Manoeuvring from Data slot/sheets view to canvas view of a specific screen/component requires users to first click Project Map tab, search for the block and double click on it. This may induce excessive actions from users when switching in between these two views frequently, e.g., designing on the canvas while checking the data back and forth.
This design is to have the canvas integrated into the tab view to achieve a more consistent interface. Hover on the tab, you can find a dropdown menu of available blocks for fast switching between different views (without always returning to the project map). The dropdown menu also features "recent" items.