How to disable long press Caps Lock feature in Mac keyboard?
This is only a partial answer to your question.

You can disable the built-in behaviour of the Caps Lock key so that the light won't turn on, and it won't make your typing all uppercase, no matter whether you tap it or hold it down. After making this change the Caps Lock key will do nothing at all, and that means it won't switch input sources either.


Open System Preferences
Open the Keyboard Preferences
Press the button for "Modifier Keys..."
Select Keyboard "Apple Internal Keyboard"
Change "Caps Lock (⇪) Key" to "No Action".




I understand this isn't quite you want -- you want Caps Lock to be used only for switching languages, never for uppercase text. Maybe it's possible to combine this with some other tool that installs a custom behaviour for the Caps Lock key.