I always thought global disable/enable of Overwrite was done by pressing the "Insert" key on the keyboard but maybe this is different in Windows 10.
Nope. It's still the Insert key and that key is a toggle. But, Insert as toggle is not turned on by default and neither is using overtype mode. You have to do the following in existing documents, or to your normal document template if you wish this to be in effect in any new blank document you create:
To change the overtype settings so that you can access overtype mode by pressing INSERT, do the following:
Press Alt+F, T to open Word Options.
Press A to select ADVANCED, and then press Tab.
Press Alt+O to move to the Use the Insert key to control overtype mode check box.
Press the Spacebar to select the check box, and then press Enter.
To turn Overtype mode on or off, press INSERT.
Brian AKA Bri the Tech Guy (website in my user profile) - Windows 10 Home, 64-Bit, Version 1809, Build 17763
Presenting the willfully ignorant with facts is the very definition of casting pearls before swine.
~ Brian Vogel