EndNote 20 marks a change in naming conventions from previous versions, which used the Roman number X (eg: X9 meant EndNote 19).
Some other big changes are:
There are only 5 icons now, with new reference and share library being the most prominent.
In previous versions of EndNote you could arrange the preview window in different ways, such as on the bottom of the screen. The preview window now always lives on the right of screen.
It always appears above your reference library now.
The PDF tab has been removed and the PDF preview option is now included in the summary area. To open the PDF, click on the drop down arrow next to the PDF title; you have the choice of opening the PDF in EndNote's viewer or in Adobe (we recommend EndNote's viewer).
Previously this option lived under Edit
If you open Word first, then EndNote, you won't see this toolbar in Word.
In the past you would have to close the edit mode or click out of the reference, at which point EndNote would ask if you wanted to save.
Previously this option was initiated by right clicking on a reference or scrolling to the bottom of the list of field names when editing a reference (this second option is still available).
Previously this was always displayed at the bottom of the preview window.
The button doesn't appear until you mouse over the right area (seen below). You can also access preferences via Edit > Preferences (Windows) or EndNote 20 > Preferences (Mac).