Rust drip in the inside of the toilet bowl
The Works Toilet Bowl cleaner is the only thing I know of that might get that out
Scrub it with a pumice stone.
I agree, turn off the water to the toilet and flush until the water has drained. Scrub the rust spot with a pumice stone. This should remove the rust stain. There is also a product called Rust Out, but it can only be used on white surfaces. It will discolor anything but white.
have you tried denture cleaner?
The rust is not the bowl itself, so sooner or later, the source of the rust must be stopped.
If it’s your entire tap water system then invest in a whole house water filter (not a water softener) for about $70 for your health.
Check your tank. You can clean the rust and replace any rusty parts. A can of coke poured in the toilet bowl will help remove the rust.