TMPro, MRTK, 'RectMask2D does not contain a definition for 'padding' - Help?

I'm setting up a project for Hololens as per the instructions here: https://docs.microsoft.com/en-us/windows/mixed-reality/develop/unity/tutorials/mr-learning-base-02?tabs=winxr

Using Unity version 2019.4.10f1. After importing the TMPro Essential Resources, everything is working okay. However then I import the MRTK Foundation (via the Microsoft Mixed Reality Feature Tool), and I get the following error:

Library\PackageCache\com.unity.textmeshpro@2.1.4\Scripts\Runtime\TMP_DefaultControls.cs(188,22): error CS1061: 'RectMask2D' does not contain a definition for 'padding' and no accessible extension method 'padding' accepting a first argument of type 'RectMask2D' could be found (are you missing a using directive or an assembly reference?)

The TMP version is 2.1.4.

I've attempted to start over, and install a lower TMP version (2.1.3), but after importing the MRTK stuff TMP upgrades itself to 2.1.4.

Any advice please?