What can I use to clean glass shower doors that are extremely stained?

https://www.hometalk.com/diy/clean/bathroom/remove-soap-scum-with-a-grapefruit-and-kosher-salt-28708364?r=1

It could be that the glass is etched. Happened to me with exterior windows that had been it by the sprinkler system for years. Couldn't get them clean, had to replace them. Sorry if that's the case. You could put one of those window films on the exterior to hide the cloudiness and make it look like it was on purpose. Lowes and Home Depot sell them.

barkeepers friend stove top liquid. Scrub quite hard. It took me days but it all came out. Nothing else worked for me. Once you get it all off, after every shower we spray with Daily Shower. It works beautiful. The scrubbing part is hard, but you’ll succeed.

Since u have tried all my "go-to" remedies, I thought u were out of luck, @ first but... Both of the above suggestions r great!

Have you tried hot water mixed with equal amount of vinegar plus Dawn & baking soda?

I have had great luck with a Simoniez product called My Cleaning Secret. I have only found it on line, but it has cleaned many very stained things in my house including windows, stoves and counters.

Get rid of grime on the interior of your glass shower door by following these simple steps:

1. Mix one part vinegar with two parts distilled water in an empty spray bottle and shake well.
2. Spray the surface of the shower door with the solution and let it work its magic for 10 minutes.
3. Use a microfiber sponge to wipe away the grime. If you see streaks once the door has dried, use your microfiber cloth to buff them out in a circular motion.