Indigo On SUPro2021 but Not on SUPro2019

[Kanastrous]

Hi all - using both Sketchup Pro 2019 and Sketchup Pro 2021 on a Windows 10 PC and want to use Indigo (downloaded and installed today) on both, but the Indigo tool palette appears only in 2021 and does not appear anywhere as a palette or menu item in 2019

How do I get Indigo showing up and useable in both 2021 and 2019?

Thanks
K