You were so intent on finding the solution that you forgot to mention what Word Processor you were using.

As you note, there is no INS key (for some reason) and I have been unable to find any key combination that achieves that function.

The choice of WP is important, ALL of them have the option to turn Insert on or off. Check out the Menu Bar at the top to that applications window.

In Word, check the preferences/edit and look for something called Overtype mode. Uncheck it

P