Try a toilet pumice stone - they sell them on Amazon and other places. Works for me to remove that hard water ring!
I had one toilet not hooked up to the water softener. It was always orange in the bowl. Most cleaners didn’t touch it. Then I discovered The Works toilet bowl cleaner and always have this on hand. Cheap and all stores carry it. Get the old original thin formula not the thick one. You would laugh if you knew how many other weird areas I’ve used this stuff. Don’t spill on carpet....it melts it!
IRON OUT ,Zud,Comet Cleanser
I use WHINK rust remover. Sold at Walmart or Menards stores.