Thank you Greg for your suggestions. I have used F8 and F5 as you suggest. No, still no sign of movement, no errors, no effect on the TestBed text. Yet, there is a cursor flashing in the Code, and the Stepping process operates without incident (but finds no errors because there aren't any.)
When I was typing the Code I made a few unnoticed typo errors. These were detected by the Compiler and corrected, proving that the Compiler was working.

Yes, my first thought was the Keybinding but it is quite sound. I used several Key Combinations, and I also tried running the Code from a QAT button, also without success.

I know nothing about References, but I ask myself whether any essential Reference, which is part of the Office Suite and therefore NOT present on my version of Word, could be responsible.

I confirm that the Macro Security button in Developer reveals that all Macros are enabled (and warns of the danger ...).
More generally, I have many Macros all of which work correctly at present - except this one.
However, I was poking about in the VBE a few days before Copying the Macro in question and may have accidentely changed some setting. Thank you for your continued interest.