Dirt or scale?

Most of the toilet cleaers are lye (castuc compounds).

Frwater rings a mild acid (ditilled white vinegar) is far more effective.

Buy a fwew gallons and fill the bowl.
You may have to get a temporary plug to fill the bowl above the normal water line.

The are an inflatable rubber ball.

Just make it a little bit larger than the bowl exit and push it in hard enough it will stay (with the valve facing out so you can pull it back out).

Add more whiten vinegar and wait.

If you start seeing small bubbles at the ring the acid is doing its job of dissolving the water scale.

There are stronger acids that work faster, but get more dangerous to use (just diluting them must be done correctly (acid into water) to avoid boiling and splatter).

Get a pair of rubber gloves and a pumice stone. Wet the stone and gently rub the ring.

I've used a combo of brickeyee and graywings' methods. Empty most of the water out of the bowl by turning off the supply and flushing. Fill up to the ring with white vinegar. Use a few pieces of plastic wrap stretched across the opening to seal the vinegar vapor in and wait a few days. It will work faster if the room is warm. Scrub with a toilet brush to loosen the softened build-up and use the pumice stone to get anything that's left. Be sure the stone is wet when you use it.

As stated above, add elbow grease - Mr Clean Magic Eraser & scrub

Just be aware that the color is only glaze deep.

Didn't know that, brickeyee. Sounds like vinegar, maybe several treatments, is the way to go.

Toilets start off as white porcelain.

Colored glaze is applied and fired on.

While pumice stones themselves are rather soft, a single grain of sand embedded in the stone (you threw it in the drawer or cabinet bottom, remember?) will scratch through the color coat.

It makes a dirty ring look minor.

My housekeeper used pumice on the ring and now we have an etched ring which is impossible to kep clean.

Oh let me tell you, my housekeeper turned me on to this !!!!! It’s drywall sandpaper/screen. I bought a 5 pack for about 7 bucks, lasts a lifetime, it is truly miraculous!