It was easy. I finally got some vinegar and filled it up and let the kettle sit overnight. Rinsed it and gave it a wipe with a wad of paper towel and the scale and residue from the scale is all gone.
Shoulda done it earlier. The wasted psychic energy, every time I peered in and saw the scale…
Our water is so hard here I periodically take the kettle into the shop when it doesn’t boil water very quick, and use the needle scaler on it to knock big slabs of scale out of it.