See on this link all new features and additional content of Power & Revolution 2020 Edition:
http://www.power-and-revolution.com/store_p21.php

If you already own the Power & Revolution 2020 Edition game, get a big discount on the price by buying the Bundle "Power & Revolution 2021 + 2021 Edition Bundle"

Additional information: if you own DLCs of the Power & Revolution 2020 Edition game, and that the same DLCs are available in the 2021 Edition, then they will automatically be taken into account and still active in your new Power & Revolution 2021 Edition game.