I have installed Discover 2021, and the option to Generate Plans in the Drillholes>Generate Sections tool is gone

You should have 2 new menu options in Discover 2021 next to Generate Section, Generate Plans and Batch Generate Sections.

If these menu options are missing, you will need to manually reset your menus by -

1. Close MapInfo Discover

2. Delete the folder -

C:\Users\USERNAME\AppData\Roaming\Encom\Discover\Ribbons

3. Start MapInfo Discover and your menu will automatically be reset.