I've updated my GSE to the latest version, and I've deleted my WTF folder to start over. After install GSE from Curse and the Druid macros, GSE does not save the check mark 'ActionButtonUseKeyDown' CVAR variable. Everytime I reload or exit the game and come back, I have to re-select that checkmark.

Please advise.

As this is a WoW CVar and not a GSE setting you need to look at what all your other mods are doing. For example some ElvUI and bartender builds set this on login a particular way. GSE can’t control whst another mod does.

Closing this as done as the OP has been supplied none of the information required for either a Bug or Enhancement. At best this is a question that should be raised as a discussion.